Medical device and method for detecting atrioventricular block

ABSTRACT

A medical device includes a motion sensor configured to sense a motion signal. The medical device includes a control circuit configured to determine at least one ventricular event metric from the motion signal sensed over multiple of atrial cycles, determine that the ventricular event metric meets atrioventricular block criteria and generate an output in response to determining the atrioventricular block.

REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Patent Application No.63/006,208 filed provisionally on Apr. 7, 2020, incorporated herein byreference in its entirety.

TECHNICAL FIELD

This disclosure relates to a medical device and method for determiningatrioventricular block.

BACKGROUND

During normal sinus rhythm (NSR), the heartbeat is regulated byelectrical signals produced by the sino-atrial (SA) node located in theright atrial wall. Each atrial depolarization signal produced by the SAnode spreads across the atria, causing the depolarization andcontraction of the atria, and arrives at the atrioventricular (AV) node.The AV node responds by propagating a ventricular depolarization signalthrough the bundle of His of the ventricular septum and thereafter tothe bundle branches and the Purkinje muscle fibers of the right and leftventricles, sometimes referred to as the “His-Purkinje system.”

Patients with a conduction system abnormality, e.g., SA node dysfunctionor poor AV node conduction, bundle branch block, or other conductionabnormalities, may receive a pacemaker to restore a more normal heartrhythm. A single chamber pacemaker coupled to a transvenous leadcarrying electrodes positioned in the right atrium may provide atrialpacing to treat a patient having SA node dysfunction. When the AV nodeis functioning normally, single chamber atrial pacing may sufficientlycorrect the heart rhythm. The pacing-evoked atrial depolarizations maybe conducted normally to the ventricles via the AV node and theHis-Purkinje system maintaining normal AV synchrony. Some patients,however, may experience conduction abnormalities of the AV node, e.g.,partial or complete AV block. AV block may be intermittent and mayevolve over time. In the presence of high-grade AV block, atrialdepolarizations are not conducted to the ventricles on every atrialcycle. A dual chamber pacemaker may be implanted in some patients topace both the atrial and ventricular chambers and maintain AV synchrony.The dual chamber pacemaker may be coupled to a transvenous atrial leadand a transvenous ventricular lead, for placing electrodes for sensingand pacing in both the atrial and ventricular chambers. The pacemakeritself is generally implanted in a subcutaneous pocket with thetransvenous leads tunneled to the subcutaneous pocket. Intracardiacpacemakers have been introduced or proposed for implantation entirelywithin a patient's heart eliminating the need for transvenous leads. Forexample, a ventricular intracardiac pacemaker may provide sensing andpacing from within a ventricular chamber of a patient having AV block toprovide ventricular rate support.

SUMMARY

The techniques of this disclosure generally relate to a medical devicehaving a motion sensor for sensing a motion signal that includesventricular event signals corresponding to ventricular contraction(and/or relaxation) following a ventricular depolarization. The medicaldevice may be configured to determine one or more features or metricsfrom the motion signal for determining when AV block may be present. Themedical device may be a pacemaker configured to deliver atrial pacingand may determine when AV block associated with less than oneventricular event signal occurring with each atrial cycle may bepresent. In some examples, the medical device is an atrial intracardiacpacemaker or a pacemaker coupled to a transvenous atrial lead such thatthe motion sensor is positioned in an atrial chamber for sensing anintra-atrial motion signal. A medical device operating according to thetechniques disclosed herein determines when AV block may be presentbased on a motion signal sensed from an atrial location in someexamples.

In one example, the disclosure provides a medical device including amotion sensor configured to sense a motion signal and a control circuitcoupled to the motion sensor for receiving the motion signal. Thecontrol circuit may be configured to determine at least one ventricularevent metric from the motion signal sensed over multiple atrial cyclesand determine if one or more ventricular event metrics meet AV blockcriteria. The control circuit generates an output in response todetermining that the AV block criteria are met by the ventricular eventmetric(s). The output may be stored in a memory of the medical deviceand subsequently used to transmit data, adjust cardiac signal sensingand/or adjust a therapy in various examples.

In another example, the disclosure provides a method including sensing amotion signal, determining at least one ventricular event metric fromthe motion signal sensed over multiple atrial cycles, and determiningthat one or more ventricular event metrics meet AV block criteria. Themethod further includes generating an output in response to determiningthe AV block criteria are met by the ventricular event metric(s). Themethod may further include storing the output in a memory andsubsequently use the stored output to transmit data, adjust cardiacsignal sensing and/or adjust a therapy in various examples.

In another example, the disclosure provides a non-transitory,computer-readable storage medium comprising a set of instructions which,when executed by a control circuit of a medical device, cause themedical device to sense a motion signal, determine at least oneventricular event metric from the motion signal sensed over multipleatrial cycles, and determine that one or more ventricular event metricsmeet AV block criteria. The instructions further cause the medicaldevice to generate an output in response to the AV block criteria beingmet by the ventricular event metric(s). The instructions may cause thedevice to store the output in memory of the medical device andsubsequently use the output to transmit data, adjust cardiac signalsensing and/or adjust a therapy in various examples.

Further disclosed herein is the subject matter of the following clauses:

1. A medical device comprising:

a motion sensor configured to sense a motion signal;

a control circuit configured to:

-   -   determine at least one ventricular event metric from the motion        signal sensed over a plurality of atrial cycles;    -   determine that the at least one ventricular event metric meets        atrioventricular block criteria; and    -   generate an output in response to determining that the        ventricular event metric meets the atrioventricular block        criteria; and

a memory configured to store the generated output.

2. The medical device of clause 1, wherein the control circuit isconfigured to determine the at least one ventricular event metric bydetermining an integration metric based on sample point amplitudes ofthe motion signal during at least a portion of each atrial cycle of theplurality of atrial cycles.3. The medical device of clause 2, wherein the control circuit isconfigured to determine the integration metric by one of:

determining a summation of amplitudes of sample points of the motionsignal sensed over the plurality of atrial cycles; and

determining a count of sample points of the motion signal sensed overthe plurality of atrial cycles that are greater than a thresholdamplitude.

4. The medical device of any of clauses 2-3, further comprising:

a sensing circuit configured to sense a cardiac electrical signal andsense P-waves from the cardiac electrical signal; and

a pulse generator configured to generate atrial pacing pulses;

wherein the control circuit is configured to:

-   -   determine a count of the plurality of atrial cycles based on at        least one of the P-waves sensed by the sensing circuit and the        atrial pacing pulses generated by the pulse generator; and    -   determine the ventricular event metric by dividing the        integration metric by the count of the plurality of atrial        cycles.        5. The medical device of any of clauses 2-4, wherein the control        circuit is further configured to:

establish a ventricular event threshold by:

-   -   determining the integration metric for each of a plurality of        integration intervals; and    -   setting the ventricular event threshold based on the determined        integration metrics;

wherein determining that the at least one ventricular event metric meetsthe atrioventricular block criteria comprises determining that at leastone integration metric determined from the motion signal sensed over theplurality of atrial cycles is less than the ventricular event threshold.

6. The medical device of any of clauses 1-5, wherein the control circuitis configured to:

determine at least one of a time of day, an atrial rate, a patientphysical activity level, and a patient posture;

set a detection time interval based on at least one of the time of day,the atrial rate, the patient physical activity level, and the patientposture, where the motion signal is sensed over the plurality of atrialcycles occurring during the detection time interval.

7. The medical device of any of clauses 1-6, wherein the control circuitis configured to:

determine at least one feature of the motion signal during each atrialcycle of the plurality of cycles;

determine each atrial cycle of the plurality of atrial cycles as one ofan atrioventricular block cycle or an atrioventricular conduction cyclebased on the at least one feature of the motion signal;

determine the ventricular event metric by determining a count of theatrioventricular block cycles; and

determine that the ventricular event metric meets atrioventricular blockcriteria in response to the count of atrioventricular block cycles beinggreater than a threshold value.

8. The medical device of clause 7, wherein the control circuit isconfigured to determine each atrial cycle of the plurality atrial cyclesas one of an atrioventricular block cycle or an atrioventricularconduction cycle by:

setting a sensing window during a portion of the atrial cycle;

determining the atrial cycle as an atrioventricular block cycle inresponse to the motion signal not meeting ventricular event criteriaduring the sensing window; and

determining the atrial cycle as an atrioventricular conduction cycle inresponse to the motion signal meeting the ventricular event criteriaduring the sensing window.

9. The medical device of any of clauses 7-8, wherein the control circuitis configured to determine each atrial cycle of the plurality of atrialcycles as one of an atrioventricular block cycle or an atrioventricularconduction cycle by:

determining the atrial cycle as an atrioventricular block cycle inresponse to determining that the motion signal crosses a ventricularevent sensing threshold amplitude less than a threshold number of timesduring the atrial cycle; and

determining the atrial cycle as an atrioventricular conduction cycle inresponse to determining that the motion signal crosses the ventricularevent sensing threshold amplitude at least the threshold number of timesduring the atrial cycle.

10. The medical device of any of clauses 1-9, wherein the controlcircuit is configured to:

establish a ventricular event morphology template from the motionsignal;

determine a morphology match score between the ventricular eventmorphology template and the motion signal sensed during a portion ofeach atrial cycle of the plurality of atrial cycles; and

determine the ventricular event metric based on the determinedmorphology match scores.

11. The medical device of any of clauses 1-10, further comprising:

a sensing circuit configured to sense a cardiac electrical signal;

wherein the control circuit is further configured to:

-   -   detect an altered morphology of an atrial P-wave sensed by the        sensing circuit; and    -   determine the atrioventricular block criteria are met in        response to detecting the altered P-wave morphology.        12. The medical device of any of clauses 1-11, wherein the        control circuit is configured to determine the at least one        ventricular event metric by determining from the motion signal        at least one of: a maximum peak amplitude, a maximum slope, a        signal area, a signal width, a count of sample points greater        than a threshold amplitude, a number of threshold crossings, or        a number of peaks.        13. The medical device of any of clauses 1-12, wherein the        control circuit is configured to determine the at least one        ventricular event metric from the motion signal by:

determining a fiducial point of the motion signal during each atrialcycle of the plurality of atrial cycles;

for each atrial cycle of the plurality of atrial cycles, determining anatrioventricular activation time from an atrial event to the fiducialpoint of the motion signal; and

determining the ventricular event metric based on the atrioventricularactivation times determined over the plurality of atrial cycles.

14. The medical device of clause 13, wherein the control circuit isfurther configured to:

determine the ventricular event metric by determining an increasingtrend of the atrioventricular activation time and at least onepreviously determined atrioventricular activation time; and

determine that the ventricular event metric meets the atrioventricularblock criteria in response to determining the increasing trend of theatrioventricular activation time.

15. The medical device of any of clauses 1-14, wherein the controlcircuit is further configured to:

set an atrial blanking window during each atrial cycle of the pluralityof atrial cycles; and

determine the ventricular event metric from the motion signal sensedoutside the atrial blanking windows.

16. The medical device of any of clauses 1-15, further comprising:

a sensing circuit configured to sense a cardiac electrical signal andsense far-field R-waves from the cardiac electrical signal;

wherein the control circuit is configured to:

-   -   determine a loss of far-field R-wave sensing by the sensing        circuit; and    -   determine the ventricular event metric from the motion signal        over the plurality of atrial cycles in response to determining        the loss of far-field R-wave sensing.        17. The medical device of any of clauses 1-16, further        comprising a sensing circuit configured to:

sense a cardiac electrical signal; and

enable sensing of far-field R-waves from the cardiac electrical signalin response to the control circuit generating the output.

18. The medical device of any of clauses 1-17, further comprising apulse generator configured to adjust a pacing therapy in response to thecontrol circuit generating the output.

19. The medical device of any of clauses 1-18, further comprising:

a sensing circuit configured to sense a cardiac electrical signal;

a memory; and

a telemetry circuit;

wherein the control circuit is configured to generate the output bystoring an episode of at least one of the cardiac electrical signal andthe motion signal in response to determining the atrioventricular blockcriteria are met; and

the telemetry circuit is configured to transmit the stored episode.

20. The medical device of any of clauses 1-19, wherein the controlcircuit is configured to:

detect a condition for monitoring for atrioventricular block; and

determine the at least one ventricular event metric from the motionsignal in response to detecting the condition for monitoring foratrioventricular block.

21. The medical device of clause 20, wherein the control circuit isfurther configured to set the atrioventricular block criteria based onthe detected condition for monitoring for atrioventricular block.

22. The medical device of any of clauses 1-21, wherein the controlcircuit is further configured to:

determine that the motion signal meets termination criteria afterdetermining that the at least one ventricular event metric meets theatrioventricular block criteria; and

determining a duration of atrioventricular block in response to thetermination criteria being met.

23. The medical device of any of clauses 1-22, further comprising asensing circuit configured to sense a cardiac electrical signal, andwherein:

the control circuit is configured to:

-   -   determine the at least one ventricular event metric by        determining an integration metric from the motion signal over        each one of a plurality of integration intervals;    -   determine that a first one of the determined integration metrics        is less than or equal to an atrioventricular block threshold;    -   start storing a cardiac signal episode in the memory by storing        at least one of the motion signal and the cardiac electrical        signal in response to determining that the first one of the        determined integration metrics is less than or equal to the        atrioventricular block threshold;    -   determine that the at least one ventricular event metric meets        the atrioventricular block criteria by:        -   determining a representative value of the integration            metrics determined over each one of the plurality of            integration intervals; and        -   determining that the representative value is less than or            equal to the atrioventricular block threshold; and    -   generate the output by storing the cardiac signal episode        extending through at least a portion of the plurality of        integration intervals as an atrioventricular block episode in        the memory.        24. A method, comprising:

sensing a motion signal;

determining at least one ventricular event metric from the motion signalsensed over a plurality of atrial cycles;

determining that the at least one ventricular event metric meetsatrioventricular block criteria;

generating an output in response to determining the atrioventricularblock criteria are met; and

storing the generated output.

25. The method of clause 24, wherein determining the at least oneventricular event metric comprises determining an integration metricbased on sample point amplitudes of the motion signal during at least aportion of each atrial cycle of the plurality of atrial cycles.26. The method of clause 25, wherein determine the integration metriccomprises one of: determining a summation of amplitudes of sample pointsof the motion signal sensed over the plurality of atrial cycles; anddetermining a count of sample points of the motion signal sensed overthe plurality of atrial cycles that are greater than a thresholdamplitude.27. The method of any of clauses 25-26, further comprising:

sensing a cardiac electrical signal;

sensing P-waves from the cardiac electrical signal;

generating atrial pacing pulses;

determining a count of the plurality of atrial cycles based on at leastone of the sensed P-waves and the atrial pacing pulses; and

determining the ventricular event metric by dividing the integrationmetric by the count of the plurality of atrial cycles.

28. The method of any of clauses 25-27, further comprising:

establishing a ventricular event threshold by:

-   -   determining the integration metric for each of a plurality of        integration intervals; and    -   setting the ventricular event threshold based on the determined        integration metrics;

wherein determining that the at least one ventricular event metric meetsthe atrioventricular block criteria comprises determining that at leastone integration metric determined from the motion signal sensed over theplurality of atrial cycles is less than the ventricular event threshold.

29. The method of any of clauses 24-28, further comprising:

determining at least one of a time of day, an atrial rate, a patientphysical activity level, and a patient posture;

setting a detection time interval based on at least one of the time ofday, the atrial rate, the patient physical activity level, and thepatient posture, where the motion signal is sensed over the plurality ofatrial cycles occurring during the detection time interval.

30. The method of any of clauses 24-29, further comprising:

determining at least one feature of the motion signal during each atrialcycle of the plurality of cycles;

determining each atrial cycle of the plurality of atrial cycles as oneof an atrioventricular block cycle or an atrioventricular conductioncycle based on the at least one feature of the motion signal;

determining the ventricular event metric by determining a count of theatrioventricular block cycles; and

determining that the ventricular event metric meets atrioventricularblock criteria in response to the count of atrioventricular block cyclesbeing greater than a threshold value.

31. The method of clause 30, wherein determining each atrial cycle ofthe plurality of atrial cycles as one of an atrioventricular block cycleor an atrioventricular conduction cycle comprises:

setting a sensing window during the atrial cycle;

determining the atrial cycle as an atrioventricular block cycle inresponse to the motion signal not meeting ventricular event criteriaduring the sensing window; and

determining the atrial cycle as an atrioventricular conduction cycle inresponse to the motion signal meeting the ventricular event criteriaduring the sensing window.

32. The method of any of clauses 30-31, wherein determining each atrialcycle of the plurality of atrial cycles as one of an atrioventricularblock cycle or an atrioventricular conduction cycle comprises:

determining the atrial cycle as an atrioventricular block cycle inresponse to determining that the motion signal crosses a ventricularevent sensing threshold amplitude less than a threshold number of timesduring the atrial cycle; and

determining the atrial cycle as an atrioventricular conduction cycle inresponse to determining that the motion signal crosses the ventricularevent sensing threshold amplitude at least the threshold number of timesduring the atrial cycle.

33. The method of any of clauses 24-32, further comprising:

establishing a ventricular event morphology template from the motionsignal;

determining a morphology match score between the ventricular eventmorphology template and the motion signal sensed during a portion ofeach atrial cycle of the plurality of atrial cycles; and

determining the ventricular event metric based on the determinedmorphology match scores.

34. The method of any of clauses 24-33, further comprising:

sensing a cardiac electrical signal;

detecting an altered morphology of an atrial P-wave sensed from thecardiac electrical signal; and

determining the atrioventricular block criteria are met in response todetecting the altered P-wave morphology.

35. The method of any of clauses 24-34, wherein determining the at leastone ventricular event metric comprises determining from the motionsignal at least one of: a maximum peak amplitude, a maximum slope, asignal area, a signal width, a count of sample points greater than athreshold amplitude, a number of threshold crossings, or a number ofpeaks.36. The method of any of clauses 24-35, wherein determining the at leastone ventricular event metric from the motion signal comprises:

determining a fiducial point of the motion signal during each atrialcycle of the plurality of atrial cycles;

for each atrial cycle of the plurality of atrial cycles, determining anatrioventricular activation time from an atrial event to the fiducialpoint of the motion signal; and

determining the ventricular event metric based on the atrioventricularactivation times determined over the plurality of atrial cycles.

37. The method of clause 36, further comprising:

determining the ventricular event metric by determining an increasingtrend of the atrioventricular activation time and at least onepreviously determined atrioventricular activation time;

and

determining that the ventricular event metric meets the atrioventricularblock criteria in response to determining the increasing trend of theatrioventricular activation time.

38. The method of any of clauses 24-37, further comprising:

setting an atrial blanking window during each atrial cycle of theplurality of atrial cycles; and

determining the ventricular event metric from the motion signal sensedoutside the atrial blanking windows.

39. The method of any of clauses 24-38, further comprising:

sensing a cardiac electrical signal;

sensing far-field R-waves from the cardiac electrical signal;

determining a loss of far-field R-wave sensing from the cardiacelectrical signal; and

determining the ventricular event metric from the motion signal over theplurality of atrial cycles in response to determining the loss offar-field R-wave sensing.

40. The method of any of clauses 24-39, further comprising:

sensing a cardiac electrical signal; and

enabling sensing of far-field R-waves from the cardiac electrical signalin response to the control circuit generating the output.

41. The method of any of clauses 24-40, further comprising adjusting apacing therapy in response to generating the output.

42. The method of any of clauses 24-41, further comprising:

sensing a cardiac electrical signal;

generating the output by storing an episode of at least one of thecardiac electrical signal and the motion signal in response todetermining the atrioventricular block criteria are met; and

transmitting the stored episode.

43. The method of any of clauses 24-42, further comprising:

detecting a condition for monitoring for atrioventricular block; and

determining the at least one ventricular event metric from the motionsignal in response to detecting the condition for monitoring foratrioventricular block.

44. The method of clause 43, further comprising setting theatrioventricular block criteria based on the detected condition formonitoring for atrioventricular block.

45. The method of any of clauses 24-44, further comprising:

determining that the motion signal meets termination criteria afterdetermining that the at least one ventricular event metric meets theatrioventricular block criteria; and

determining a duration of atrioventricular block in response to thetermination criteria being met.

46. The method of any of clauses 24-45, further comprising:

sensing a cardiac electrical signal;

determining the at least one ventricular event metric by determining anintegration metric from the motion signal over each one of a pluralityof integration intervals;

determining that a first one of the determined integration metrics isless than or equal to an atrioventricular block threshold;

starting storage of a cardiac signal episode in the memory by storing atleast one of the motion signal and the cardiac electrical signal inresponse to determining that the first one of the determined integrationmetrics is less than or equal to the atrioventricular block threshold;

determining that the at least one ventricular event metric meets theatrioventricular block criteria by:

-   -   determining a representative value of the integration metrics        determined over each one of the plurality of integration        intervals; and    -   determining that the representative value is less than or equal        to the atrioventricular block threshold; and

generating the output by storing the cardiac signal episode extendingthrough at least a portion of the plurality of integration intervals asan atrioventricular block episode in the memory.

47. A non-transitory, computer-readable storage medium comprising a setof instructions which, when executed by a control circuit of a medicaldevice, cause the medical device to:

sense a motion signal;

determine at least one ventricular event metric from the motion signalsensed over a plurality of atrial cycles;

determine that the at least one ventricular event metric meetsatrioventricular block criteria;

generate an output in response to determining the atrioventricularblock; and

store the output in a memory of the medical device.

The details of one or more aspects of the disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the techniques described in this disclosurewill be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an implantable medicaldevice (IMD) system that may be used to sense cardiac electrical signalsand cardiac mechanical signals induced by cardiac motion and flowingblood and provide pacing therapy to a patient's heart.

FIG. 2 is a conceptual diagram of the atrial pacemaker shown in FIG. 1 .

FIG. 3 is a conceptual diagram of an atrial pacemaker according toanother example.

FIG. 4 is conceptual diagram of the pacemaker of FIG. 3 shown implantedin the RA at an implant site for providing dual chamber pacing andsensing according to one example.

FIG. 5 is a conceptual diagram of a medical device system capable ofpacing a patient's heart and sensing cardiac electrical signals andcardiac motion signals for determining AV block according to anotherexample.

FIG. 6 is a conceptual diagram of an example configuration of the atrialpacemaker shown in FIG. 1 .

FIG. 7 is a flow chart of a method performed by a medical device fordetecting AV block from an intra-atrial motion signal according to oneexample.

FIG. 8 is a flow chart of a method performed by a pacemaker fordetecting AV block according to another example.

FIG. 9 is an example of a cardiac electrical signal and correspondingaccelerometer axis signals that may be produced by a medical device fromsignals sensed from the patient's heart during AV conduction.

FIG. 10 is diagram of a cardiac electrical signal and accelerometer axissignals that may be produced by a pacemaker during AV block.

FIG. 11 is a flow chart of a method that may be performed by a medicaldevice for detecting ventricular events according to another example.

FIG. 12 is a diagram of cardiac signals that may be sensed by apacemaker in another example.

FIG. 13 is a diagram of a cardiac electrical signal and accelerometeraxis signals during AV block.

FIG. 14 is a flow chart of a method performed by a pacemaker fordetecting AV block according to another example.

FIG. 15 is a flow chart of a method performed by a medical device, e.g.,such as a pacemaker, for detecting AV block according to anotherexample.

FIG. 16 is a diagram of a cardiac electrical signal and motion signalspanning a detection time interval according to one example.

FIG. 17 is a diagram of a cardiac electrical signal and motion signalover multiple integration intervals for determining a ventricular eventmetric according to one example.

FIG. 18 is a histogram of integration metrics, each determined over anintegration interval, e.g., as described in conjunction with FIG. 16 or17 .

FIG. 19 is a flow chart of a method for determining AV block andgenerating an output by a medical device according to another example.

FIG. 20 is a flow chart of a method for determining AV block criteriaare met by at least one ventricular event metric and generating anoutput in response to the AV block criteria being met according toanother example.

FIG. 21 is a flow chart of a method for determining when AV blockcriteria are met based on ventricular event metrics determined asintegration metrics from the motion signal and generating an AV blockoutput in response to the integration metrics meeting the AV blockcriteria according to one example.

DETAILED DESCRIPTION

In general, this disclosure describes techniques for determining when AVblock criteria are met from a sensor signal that includes ventricularevent signals corresponding to ventricular contraction. The sensor maybe implanted in an atrial location, e.g., in or on an atrium, forsensing a signal correlated to mechanical heart activity. The sensor maybe a motion sensor such as an accelerometer, a pressure sensor, a flowsensor or other sensor or combination thereof capable of generating asignal that includes ventricular event signals corresponding to themechanical activation (contraction) of the ventricles. As describedbelow, a motion signal, such as an accelerometer signal, may be producedby a motion sensor implanted in or on an atrial chamber. The motionsignal may include cardiac event signals attendant to the mechanicalcontractions of the heart chambers. For example, ventricular mechanicalevent signals corresponding to ventricular contraction and/or closure ofthe atrioventricular valves caused by ventricular contraction may bepresent in a motion signal produced by a motion sensor implanted at anon-ventricular location, e.g., in or on an atrial chamber. A medicaldevice operating according to the techniques disclosed herein may senseventricular mechanical events, also referred to herein as “ventricularevents,” e.g., ventricular systolic events corresponding to ventricularcontraction and/or ventricular diastolic events correspondingventricular relaxation and filling, from a motion sensor signal anddetect AV conduction in response to sensing the ventricular mechanicalevents or detect AV block, or suspected AV block, when sensing of theventricular mechanical events do not meet AV conduction criteria. AVblock may be detected by the medical device when the motion signal meetsAV block detection criteria over multiple atrial cycles.

As described below, a medical device including a motion sensor may beconfigured to determine a ventricular event metric from the motionsensor signal sensed over multiple atrial cycles and determine when oneor more ventricular event metrics meet AV block criteria. As usedherein, the term “ventricular event metric” refers to a value determinedby the medical device from a sensor signal, e.g., a motion signal suchas an acceleration signal sensed by an accelerometer, that is correlatedto the strength (amplitude), frequency (or rate) and/or regularity(relative to atrial events) of the ventricular event signals in thesensor signal over multiple atrial cycles. The ventricular event metricmay be determined as a count of sensed ventricular event signals overmultiple atrial cycles, a ratio of sensed ventricular events to atrialevents, an integration of the motion signal over multiple atrial cycles,an AV activation time, or variability of the AV activation time, asexamples. Other examples of ventricular event metrics that may bedetermined from a sensor signal over multiple atrial cycles fordetermining when AV block criteria are met are described herein.

As used herein, the term “AV block criteria” refers to one or morethresholds or other criteria that may be applied to one or moreventricular event metrics or values derived from the ventricular eventmetrics to discriminate between episodes of relatively low ventricularmotion and episodes of relatively higher ventricular motion. Theepisodes of relatively low ventricular motion, or more generally lowcardiac motion, may correspond to episodes of AV block. Episodes ofrelatively higher cardiac motion as determined based on the ventricularevent metric(s) may correspond to episodes of AV conduction. Variousexamples of AV block criteria are described below as they pertain todifferent types of ventricular event metrics that may be determined bythe medical device.

In some examples, the medical device is an atrial pacemaker, which maybe wholly implantable within an atrial heart chamber, having a motionsensor for producing an intra-atrial motion signal. Ventricular eventsignals may be sensed from within the atrium from the motion sensorsignal for determining when AV block criteria are met, without requiringa sensor in or on the ventricles of the patient's heart for sensingventricular events. Atrial P-waves, and in some examples far fieldventricular R-waves, may be sensed using electrodes carried by theatrial pacemaker, and atrial pacing pulses can be delivered by thepacemaker implanted in the atrium. In some examples, the atrialpacemaker may be configured to pace the ventricular conduction system,e.g., the His-Purkinje system, from a location within the right atriumto provide ventricular pacing, which may track the atrial rate. In otherexamples, the atrial pacemaker may be implanted outside the heart andcoupled to an epicardial or transvenous lead for positioning electrodesfor sensing atrial P-waves and delivering atrial pacing pulses. The leadmay carry a motion sensor for sensing a cardiac motion signal that mayinclude ventricular event signals.

FIG. 1 is a conceptual diagram illustrating an implantable medicaldevice (IMD) system 10 that may be used to sense cardiac electricalsignals and cardiac mechanical signals induced by cardiac motion andflowing blood and provide pacing therapy to a patient's heart 8. IMDsystem 10 includes an atrial pacemaker 14. Pacemaker 14 may be aleadless, transcatheter intracardiac pacemaker which is adapted forimplantation wholly within a heart chamber, e.g., wholly within theright atrium (RA) of heart 8 for sensing cardiac signals and deliveringatrial pacing pulses. Pacemaker 14 may be reduced in size compared tosubcutaneously implanted pacemakers and may be generally cylindrical inshape to enable transvenous implantation via a delivery catheter.Pacemaker 14 is shown positioned in the RA, e.g., along an endocardialwall though other locations are possible within or on the RA differentthan the location shown. The techniques disclosed herein are not limitedto a particular intra-atrial pacemaker location.

Pacemaker 14 is capable of producing electrical stimulation pulses,e.g., pacing pulses, delivered to heart 8 via one or more electrodes onthe outer housing of the pacemaker. Pacemaker 14 is configured todeliver RA pacing pulses and sense an RA cardiac electrical signal usinghousing based electrodes for producing an RA electrogram (EGM) signal.The cardiac electrical signals may be sensed using the housing basedelectrodes that are also used to deliver pacing pulses to the RA in someexamples.

Pacemaker 14 may be a leadless pacemaker as shown, includinghousing-based electrodes for sensing the cardiac electrical signal anddelivering pacing pulses. As described below, pacemaker 14 includescardiac electrical signal sensing circuitry configured to sense atrialP-waves attendant to the depolarization of the atrial myocardium and apulse generator for generating and delivering an atrial pacing pulse inthe absence of a sensed atrial P-wave. In some examples, the cardiacelectrical signal sensing circuitry of pacemaker 14 may be configured tosense far-field R-waves (FFRWs) associated with the depolarization ofthe ventricular myocardium using the housing based electrodes. Forinstance, an atrial pacing pulse may be triggered by sensing an FFRW.Examples of cardiac sensing and atrial pacing methods that may beperformed by pacemaker 14 are generally disclosed in U.S. Pat. No.9,808,633 (Bonner, et al.), incorporated herein by reference in itsentirety. For example, an atrial pacing pulse may be triggered by asensed FFRW for promoting synchrony between the atrial and ventricularheart chamber contractions.

According to the techniques described herein, ventricular eventsassociated with ventricular contraction are detected by pacemaker 14from a motion sensor signal such as an accelerometer signal, produced bya motion sensor that may be enclosed by the housing of pacemaker 14. Themotion signal produced by an accelerometer implanted within an atrialchamber, which may be referred to as an “intra-atrial motion signal,”may include motion signals caused by ventricular and atrial mechanicalevents. For example, acceleration of blood due to closure of thetricuspid valve 16 between the RA and RV, the mitral valve between theleft atrium and the left ventricle and the heart motion due toventricular contraction may produce a ventricular event signal. Asdescribed below, pacemaker 14 includes a control circuit with processingcircuitry that is configured to determine when AV block criteria aremet, e.g., due to the absence of ventricular event signals in 1:1synchrony with atrial cycles and/or a prolonged delay in the ventricularevent signal following atrial electrical events (sensed P-waves oratrial pacing pulses).

Pacemaker 14 may be configured to deliver atrial pacing therapy fortreating a sinus node dysfunction. In some patients, the AV node may befunctioning normally such that the pacing-evoked depolarizations causedby atrial pacing pulses are conducted to the ventricles by the normalconduction pathway, e.g., through the AV node and along the ventricularconduction system including the His bundle and the Purkinje fibers. Themotion sensor, e.g., an accelerometer, included in pacemaker 14 producesa signal, e.g., an acceleration signal, that includes ventricular eventsignals corresponding to ventricular mechanical activation(contraction). In this way, pacemaker 14 may be enabled to detect andverify AV conduction. Pacemaker 14 may be configured to determine whenAV block occurs or is likely to be present and may track a progressionof AV block. The progression of AV block may be tracked by pacemaker 14based on detecting an increase in the time between an atrial electricalevent and the subsequent ventricular event and/or detecting anincreasing frequency of atrial cycles in which the ventricular eventdoes not follow the atrial electrical event at an expected conductioninterval. As described below, pacemaker 14 may respond to determiningthat AV block criteria are met by generating an output, e.g., an AVblock notification or alert and/or storing a segment of the motionsensor signal and/or atrial EGM signal.

Pacemaker 14 may be capable of bidirectional wireless communication withan external device 20 for programming the sensing and pacing controlparameters, which may be utilized for detecting ventricular eventsand/or determining when AV block criteria are met from the motion sensorsignal. Aspects of external device 20 may generally correspond to theexternal programming/monitoring unit disclosed in U.S. Pat. No.5,507,782 (Kieval, et al.), hereby incorporated herein by reference inits entirety. External device 20 is often referred to as a “programmer”because it is typically used by a physician, technician, nurse,clinician or other qualified user for programming operating parametersin pacemaker 14. External device 20 may be located in a clinic, hospitalor other medical facility. External device 20 may alternatively beembodied as a home monitor or a handheld device that may be used in amedical facility, in the patient's home, or another location. Operatingparameters, including sensing and therapy delivery control parameters,may be programmed into pacemaker 14 by a user interacting with externaldevice 20.

External device 20 may include a processor 52, memory 53, display unit54, user interface 56 and telemetry unit 58. Processor 52 controlsexternal device operations and processes data and signals received frompacemaker 14. Display unit 54 may generate a display, which may includea graphical user interface, of data and information relating topacemaker functions to a user for reviewing pacemaker operation andprogrammed parameters as well as cardiac electrical signals, cardiacmotion signals or other physiological data that may be acquired bypacemaker 14 and transmitted to external device 20 during aninterrogation session. For example, pacemaker 14 may generate an outputincluding an AV block detection notification and transmit thenotification which may include data determined to support the AV blockdetection and may include an episode of the atrial EGM signal producedby pacemaker sensing circuitry and/or an episode of the motion signalproduced by the motion sensor included in pacemaker 14 when AV blockcriteria are met by the motion signal. Notification of the AV blockdetection enables a clinician to make patient management decisions,e.g., upgrading from a single atrial chamber pacing therapy to a dualchamber pacing therapy.

User interface 56 may include a mouse, touch screen, keypad or the liketo enable a user to interact with external device 20 to initiate atelemetry session with pacemaker 14 for retrieving data from and/ortransmitting data to pacemaker 14, including programmable parameters forcontrolling cardiac event sensing and therapy delivery. Telemetry unit58 includes a transceiver and antenna configured for bidirectionalcommunication with a telemetry circuit included in pacemaker 14 and isconfigured to operate in conjunction with processor 52 for sending andreceiving data relating to pacemaker functions via communication link24. Telemetry unit 58 may establish a wireless bidirectionalcommunication link 24 with pacemaker 14. Communication link 24 may beestablished using a radio frequency (RF) link such as BLUETOOTH®, Wi-Fi,Medical Implant Communication Service (MICS) or other communicationbandwidth. In some examples, external device 20 may include aprogramming head that is placed proximate pacemaker 14 to establish andmaintain a communication link 24, and in other examples external device20 and pacemaker 14 may be configured to communicate using a distancetelemetry algorithm and circuitry that does not require the use of aprogramming head and does not require user intervention to maintain acommunication link.

It is contemplated that external device 20 may be in wired or wirelessconnection to a communications network via a telemetry circuit thatincludes a transceiver and antenna or via a hardwired communication linefor transferring data to a centralized database or computer to allowremote management of the patient. Remote patient management systemsincluding a centralized patient database may be configured to utilizethe presently disclosed techniques to enable a clinician to be notifiedwhen AV block criteria are determined to be met by pacemaker 14. Reviewof AV block detection data, EGM, motion sensor signal, and markerchannel data may be performed remotely by a clinician who may authorizeprogramming of sensing and therapy control parameters in pacemaker 14,e.g., after viewing a visual representation of AV block related data,EGM, motion sensor signal and marker channel data.

FIG. 2 is a conceptual diagram of the pacemaker 14 shown in FIG. 1 .Pacemaker 14 includes electrodes 162 and 164 spaced apart along thehousing 150 of pacemaker 14 for sensing cardiac electrical signals anddelivering pacing pulses. Electrode 164 is shown as a tip electrodeextending from a distal end 102 of pacemaker 14, and electrode 162 isshown as a ring electrode along a mid-portion of housing 150, forexample adjacent proximal end 104. Distal end 102 is referred to as“distal” in that it is expected to be the leading end as pacemaker 14 isadvanced through a delivery tool, such as a catheter, and placed againsta targeted pacing site.

Electrodes 162 and 164 form an anode and cathode pair for bipolarcardiac pacing and sensing. In alternative embodiments, pacemaker 14 mayinclude two or more ring electrodes, two tip electrodes, and/or othertypes of electrodes exposed along pacemaker housing 150 for deliveringelectrical stimulation to heart 8 and sensing cardiac electricalsignals. Electrodes 162 and 164 may be, without limitation, titanium,platinum, iridium or alloys thereof and may include a low polarizingcoating, such as titanium nitride, iridium oxide, ruthenium oxide,platinum black, among others. Electrodes 162 and 164 may be positionedat locations along pacemaker 14 other than the locations shown.

Housing 150 is formed from a biocompatible material, such as a stainlesssteel or titanium alloy. In some examples, the housing 150 may includean insulating coating. Examples of insulating coatings include parylene,urethane, PEEK, or polyimide, among others. The entirety of the housing150 may be insulated, but only electrodes 162 and 164 uninsulated.Electrode 164 may serve as a cathode electrode and be coupled tointernal circuitry, e.g., a pacing pulse generator and cardiacelectrical signal sensing circuitry, enclosed by housing 150 via anelectrical feedthrough crossing housing 150. Electrode 162 may be formedas a conductive portion of housing 150 defining a ring electrode that iselectrically isolated from the other portions of the housing 150 asgenerally shown in FIG. 2 . In other examples, the entire periphery ofthe housing 150 may function as an electrode that is electricallyisolated from tip electrode 164, instead of providing a localized ringelectrode such as electrode 162. Electrode 162 formed along anelectrically conductive portion of housing 150 serves as a return anodeduring pacing and sensing.

The housing 150 may include a control electronics subassembly 152 and abattery subassembly 160, which provides power to the control electronicssubassembly 152. Control electronics subassembly 152 houses theelectronics for sensing cardiac signals, producing pacing pulses andcontrolling therapy delivery and other functions of pacemaker 14 asdescribed herein. A motion sensor may be implemented as an accelerometerenclosed within housing 150 in some examples. The accelerometer providesa signal to a processor included in control electronics subassembly 152for signal processing and analysis for detecting cardiac mechanicalevent signals, e.g., ventricular event signals, for use in detecting AVblock as described herein.

The accelerometer may be a multi-axis or multi-dimensional accelerometerwhere each axis of the accelerometer generates an acceleration signal ina different dimension. In some examples, the accelerometer may have one“longitudinal” axis that is parallel to or aligned with the longitudinalaxis 108 of pacemaker 14 and two orthogonal axes that extend in radialdirections relative to the longitudinal axis 108. Practice of thetechniques disclosed herein, however, are not limited to a particularorientation of the accelerometer within or along housing 150 or aparticular number of axes. A one-dimensional accelerometer may be usedto obtain a motion signal from which cardiac mechanical events may bedetected and a ventricular event metric may be determined. In otherexamples, a two dimensional accelerometer or other multi-dimensionalaccelerometer may be used. Each axis of a single or multi-dimensionalaccelerometer may be defined by a piezoelectric element,micro-electrical mechanical system (MEMS) device or other sensor elementcapable of producing an electrical signal in response to changes inacceleration imparted on the sensor element, e.g., by converting theacceleration to a force or displacement that is converted to theelectrical signal. In a multi-dimensional accelerometer, the sensorelements may be arranged orthogonally with each sensor element axisorthogonal relative to the other sensor element axes. Orthogonalarrangement of the elements of a multi-axis accelerometer, however, isnot necessarily required.

Each sensor element or axis may produce an acceleration signalcorresponding to a vector aligned with the axis of the sensor element. Avector signal of a multi-dimensional accelerometer (also referred toherein as a “multi-axis” accelerometer) for use in sensing cardiacmechanical events or determining cardiac event metrics may be selectedas a single axis signal or a combination of two or more axis signals.For example, one, two or all three axis signals produced by a threedimensional accelerometer may be selected for processing and analysisfor use in determining when AV block criteria are met by pacemaker 14.

Pacemaker 14 may include features for facilitating deployment andfixation of pacemaker 14 at an implant site. For example, pacemaker 14may include a set of fixation tines 166 to secure pacemaker 14 topatient tissue, e.g., by actively engaging with the atrial endocardiumand/or interacting with the atrial pectinate muscle. Fixation tines 166are configured to anchor pacemaker 14 to position electrode 164 inoperative proximity to a targeted tissue for delivering therapeuticelectrical stimulation pulses. Numerous types of active and/or passivefixation members may be employed for anchoring or stabilizing pacemaker14 in an implant position. Pacemaker 14 may optionally include adelivery tool interface 158. Delivery tool interface 158 may be locatedat the proximal end 104 of pacemaker 14 and is configured to connect toa delivery device, such as a catheter, used to position pacemaker 14 atan implant location during an implantation procedure, for example withinan atrial chamber.

FIG. 3 is a conceptual diagram of pacemaker 14 according to anotherexample. In FIG. 2 , the cathode tip electrode 164 is shown as a buttonor hemispherical type electrode that may contact the atrial endocardialtissue when distal end 102 is anchored at an implant site by fixationtines 166. In the example of FIG. 3 , the cathode tip electrode 184 isshown as a screw-in helical electrode which may provide fixation ofpacemaker 14 at the implant site as well as serving as a pacing/sensingelectrode. In the example of FIG. 3 , pacemaker 14 may be configured toprovide dual chamber pacing when electrode 184 is advanced from withinthe right atrial chamber to a His bundle pacing location or ventricularseptal pacing location.

In this case, tip electrode 184 and return anode electrode 182 may beused for pacing the ventricles, e.g., via the His bundle when AV blockis detected by pacemaker 14. A second cathode electrode 186 may beprovided at or near distal end 102 for providing atrial pacing andsensing in combination with the return anode 182 in some examples.Pacemaker 14 may include two or more electrodes which may be ringelectrodes, helical electrodes, hook electrodes, button electrodes,hemispherical electrodes or other types of electrodes arranged alonghousing 150 for providing at least atrial sensing and pacing (which mayinclude far field R-wave sensing from the atrial signal) and may furtherprovide ventricular electrical signal sensing (e.g., R-wave sensing)and/or ventricular pacing, e.g., via the His bundle, in some examples.Examples of various electrode arrangements that may be included in apacemaker configured to perform the AV block determination techniquesdisclosed herein are generally disclosed in U.S. Publication No.2019/0083779 (Yang, et al.), incorporated herein by reference in itsentirety.

FIG. 4 is conceptual diagram of the pacemaker 14 of FIG. 3 shownimplanted in the RA at an implant site for providing dual chamber pacingand sensing according to one example. The distal end 102 of pacemaker 14may be positioned at the inferior end of the interatrial septum, beneaththe AV node and near the tricuspid valve annulus to position tipelectrode 184 for advancement into the interatrial septum toward the Hisbundle. Ring electrode 182 spaced proximally from tip electrode 184 maybe used as the return electrode with the cathode tip electrode 184 forpacing the right and left ventricles via the His-Purkinje system. Thedistal ring electrode 186 may be used in combination with the proximalring electrode 182 for sensing atrial P-waves and delivering atrialpacing pulses. In this position, a motion sensor included in pacemaker14 may produce a signal including ventricular event signals. Pacemaker14 may be configured to detect or confirm AV block based on the motionsignal produced by the motion sensor. Pacemaker 14 may be configured torespond to determining that AV block criteria are met by deliveringventricular pacing pulses via electrode 184 to provide ventricular ratesupport.

FIG. 5 is a conceptual diagram of a medical device system 250 capable ofpacing a patient's heart 8 and sensing cardiac electrical signals andcardiac motion signals for determining when AV block criteria are metaccording to another example. The system 250 includes a pacemaker 254coupled to a patient's heart 8 via at least one transvenous medicalelectrical lead 266 and/or lead 268. Pacemaker 254 is shown as a dualchamber device capable of delivering cardiac pacing pulses and sensingcardiac electrical signals in an atrial chamber and in a ventricularchamber using an electrode 284 advanced from the RA to a His bundlepacing location. In other examples, pacemaker 254 may be configured assingle chamber device, e.g., coupled to only a signal lead 266 extendinginto the RA for RA sensing and pacing. Pacemaker housing 255 enclosesinternal circuitry corresponding to the various circuits and components,for example as described in conjunction with FIG. 6 below, for sensingcardiac electrical signals from heart 8, sensing cardiac motion signalsfor use in determining when AV block criteria are met, and controllingelectrical stimulation therapy, e.g., pacing therapy, delivered bypacemaker 254.

Pacemaker 254 includes a connector block 252 that may be configured toreceive the proximal ends of an atrial pacing and sensing lead 266,referred to hereafter as “atrial lead” 266, and/or a ventricular pacingand sensing lead 268, referred to hereafter as “ventricular lead” 268.Each of leads 266 and 268 are advanced transvenously for positioningelectrodes for sensing and stimulation of the atria and the ventricles,respectively. Atrial lead 266 may be positioned such that its distal endis in the vicinity of the right atrium (RA). Atrial lead 266 is equippedwith pacing and sensing electrodes, shown as a tip electrode 270 and aring electrode 272 spaced proximally from tip electrode 270. Theelectrodes 270 and 272 provide sensing and pacing in the RA and are eachconnected to a respective insulated conductor extending within theelongated body of atrial lead 266. Each insulated conductor is coupledat its proximal end to a connector carried by proximal lead connector260, and thereby electrically coupled to internal pacemaker circuitryvia connector block 252.

Atrial lead 266 may include an accelerometer 274 carried by the atriallead body for positioning within the RA for sensing cardiac motionsignals. Accelerometer 274 may produce cardiac motion signals receivedby circuitry enclosed by pacemaker housing 255 via an electricalconductor extending within the lead body to proximal connector 260.Accelerometer 274 generates a motion signal sensed from within the RA.The motion signal may include ventricular event signals, e.g., asdescribed below in conjunction with FIGS. 9 and 10 and other diagramspresented herein. The ventricular event signal may be detected byprocessing circuitry included in pacemaker 250. As described below, acardiac motion signal sensed from within the RA may be used fordetecting ventricular event signals and for detecting AV block. One ormore ventricular event metrics correlated to the strength, frequencyand/or regularity of ventricular event signal may be determined from themotion signal over multiple atrial cycles for determining when AV blockcriteria are met. In some examples, pacemaker 254 is a single chamberpacemaker coupled only to the atrial lead 266 for sensing cardiacelectrical signals, sensing cardiac motion signals, and deliveringatrial pacing pulses.

Ventricular lead 268, when included, may be advanced within the rightatrium to position electrodes 282 and 284 for pacing and sensing in thevicinity of the His bundle from a right atrial approach, as shown.Ventricular lead tip electrode 284 may be a helical electrode that maybe advanced into the inferior end of the interatrial septum, beneath theAV node and near the tricuspid valve annulus to position tip electrode284 in or proximate to the His bundle. A ring electrode 282 spacedproximally from tip electrode 284 may be used as the return electrodewith the cathode tip electrode 284 for pacing the right and leftventricles via the His-Purkinje system. While lead 268 is referred toherein as a ventricular pacing and sensing lead for delivering pacingpulses for pacing the ventricles, ventricular lead 268 may be referredto as a “His bundle pacing and sensing lead” when positioned fordelivering pacing pulses to the ventricles via the His-Purkinje systemfrom the right atrial approach.

The electrodes 282 and 284 are coupled to respective insulatedconductors extending within the elongated body of ventricular lead 268,which provide electrical connection to the proximal lead connector 264coupled to connector block 252, and electrical connection to circuitryenclosed by housing 255 is thereby achieved. Cardiac electrical signalsensing circuitry included in pacemaker 254 may receive a cardiacelectrical signal from electrodes 282 and 284 of ventricular lead 268for sensing ventricular R-waves. While atrial lead 266 and ventricularlead 268 are each shown carrying two electrodes, it is recognized thateach lead may carry one or more electrodes for providing one or moreselectable pacing and/or sensing electrode vectors, which may includebipolar combinations of electrodes carried by the respective lead orunipolar combinations of an electrode carried by the respective lead andthe pacemaker housing 255. Furthermore while atrial lead 266 is shownincluding accelerometer 274, it is understood that one or both of leads266 and 268 may include a motion sensor such as accelerometer 274 forproducing a cardiac motion signal due to acceleration forces imparted onaccelerometer 274. Accelerometer 274 may be a single or multi-axisaccelerometer as described above. Circuitry enclosed by housing 255includes processing circuitry for detecting ventricular event signalsand/or determining one or more ventricular event metrics according totechniques disclosed herein from the acceleration signal produced byaccelerometer 274 and determining when AV block criteria are met basedon ventricular event signals (or the absence thereof) and/or the one ormore ventricular event metrics.

In some examples, pacemaker 254 is configured as a dual-chamberpacemaker capable of sensing and pacing in the RA and sensingventricular R-waves and delivering atrial synchronized ventricularpacing pulses, e.g., in atrial-tracking ventricular pacing modes. Inother examples, pacemaker 254 may be coupled to a single lead advancedinto the RA for sensing both atrial and ventricular signals (e.g.,FFRWs) and delivering at least atrial pacing pulses. In still otherexamples, pacemaker 254 may be a single chamber pacing device coupledonly to ventricular lead 268. In this case, accelerometer 274 may becarried by lead 268 for positioning within the RA for detecting AVblock. Pacemaker 254 may be configured to detect AV block when AV blockcriteria are met based on an analysis of the signal received fromaccelerometer 274 for use in controlling ventricular pacing deliveredvia electrode 284, particularly when ventricular electrical signalsensing is compromised, e.g., due to noise or low signal strength.

In some cases, pacemaker 254 may be configured for dual chamber sensingof both atrial electrical signals and ventricular electrical signals. AVblock may be detected based on the accelerometer signal, which mayconfirm or support AV block detection made based on electrical signalsand/or support AV block detection when electrical signals areunreliable. In response to detecting AV block, ventricular pulses may bedelivered by pacemaker 254 to for at least maintaining a minimumventricular rate and/or delivering atrial synchronized ventricularpacing. It is to be understood that in some examples, pacemaker 254 maybe configured as an implantable cardioverter defibrillator capable ofdelivering both low voltage cardiac pacing therapies and high voltagecardioversion and defibrillation (CV/DF) shocks. In this case, Pacemaker254 may be coupleable to at least one lead carrying at least one highvoltage CV/DF electrode such as an elongated coil electrode.

FIG. 6 is a conceptual diagram of an example configuration of pacemaker14 shown in FIG. 1 or FIG. 4 . FIG. 6 is described in the context ofpacemaker 14 of FIG. 1 ; however it is to be understood that circuitryand components and the associated functionality described in conjunctionwith FIG. 6 may be incorporated in pacemaker 14 shown in FIG. 4 orpacemaker 254 of FIG. 5 . Pacemaker 14 includes a pulse generator 202, acardiac electrical signal sensing circuit 204, a control circuit 206,memory 210, telemetry circuit 208, motion sensor 212 and a power source214. The various circuits represented in FIG. 6 may be combined on oneor more integrated circuit boards which include a specific integratedcircuit (ASIC), an electronic circuit, a processor (shared, dedicated,or group) and memory that execute one or more software or firmwareprograms, a combinational logic circuit, state machine or other suitablecomponents that provide the described functionality.

Motion sensor 212 may include an accelerometer in the examples describedherein. Motion sensor 212 is not limited to being an accelerometer,however, and other motion sensors may be utilized successfully inpacemaker 14 for detecting cardiac motion signals according to thetechniques described herein. Examples of motion sensors that may beimplemented in motion sensor 212 include piezoelectric sensors and MEMSdevices. Motion sensor 212 may be enclosed by the housing 150 (shown inFIG. 2 ) of leadless pacemaker 14. However, in the case of a pacemakercoupled to epicardial or transvenous leads, such as pacemaker 254 ofFIG. 5 , including a motion sensor 212 within the pacemaker housing 255may be optional. Instead a motion sensor is carried by a transvenouslead coupled to pacemaker 254, e.g., accelerometer 274 as shown in FIG.5 , for positioning within the atrial chamber for sensing intra-atrialmotion signals. In some examples, motion sensor 212 may be includedwithin the housing 255 of the pacemaker 254, in addition to a lead-basedmotion sensor, and configured for sensing motion due to patient physicalactivity and/or acceleration signal changes due to patient posturechanges.

Motion sensor 212 (or lead-based accelerometer 274) may include amulti-axis sensor, e.g., a two-dimensional or three-dimensionalaccelerometer, with each axis providing an axis signal that may beanalyzed individually or in combination for detecting cardiac mechanicalevents and determining ventricular event metrics as described below.Motion sensor 212 produces an electrical signal correlated to motion orvibration of sensor 212 (and pacemaker 14), e.g., when subjected toflowing blood and cardiac motion. The motion sensor 212 may include oneor more filter, amplifier, rectifier, analog-to-digital converter (ADC)and/or other components for producing a motion signal that is passed tocontrol circuit 206. For example, each vector signal produced by eachindividual axis of a multi-axis accelerometer may be filtered by a highpass filter, e.g., a 10 Hz high pass filter, or a bandpass filter, e.g.,a 10 Hz to 30 Hz bandpass filter. The filtered signal may be digitizedby an ADC and rectified for use by ventricular (V) event detectorcircuit 240 for detecting ventricular event signals. The high passfilter may be raised (e.g., to 15 Hz) if needed to detect ventricularevent signals that have higher frequency content. In some examples, highpass filtering is performed with no low pass filtering. In otherexamples, each accelerometer axis signal is filtered by a low passfilter, e.g., a 30 Hz low pass filter, with or without high passfiltering. Other signal processing and analysis techniques may be usedfor detecting ventricular event signals, such as fast Fourier transform,determining a differential signal, or determining a number of thresholdcrossings by the motion signal where the threshold may be greater thanor less than the amplitude of atrial event signals.

In some examples, a signal from at least one axis of an accelerometerincluded in motion sensor 212 may be passed to control circuit 206 fordetermining patient posture and/or a patient physical activity metric inaddition to using the motion signal for determining when AV blockcriteria are met, which may be used for detecting AV block (orconfirming AV conduction when AV block criteria are not met).Acceleration forces on the motion sensor 212 occur due to patientposture changes relative to gravitational acceleration forces and due topatient motion during physical activity, such as exercise and activitiesof daily living. The accelerometer axis signals may also be used fordetermining patient posture and discriminating between a horizontal ornon-upright position and non-horizontal or upright positions.

Patient posture may be determined by control circuit 206 from one ormore accelerometer axis signals for detecting AV block monitoringconditions in some examples. For instance, AV block monitoring may beperformed during daytime hours, when the patient is not asleep orresting. Control circuit 206 may detect a non-horizontal or uprightpatient posture from the accelerometer axis signals and enable AV blockmonitoring based on detecting the non-horizontal patient posture in someexamples.

A patient physical activity metric correlated to the level of physicalexertion and metabolic demand of the patient may be determined from themotion sensor signal. The patient activity metric may be used by controlcircuit 206 to detect AV block monitoring conditions. For example,control circuit 206 may enable determination of a ventricular eventmetric from the motion signal for AV block monitoring in response todetecting a patient actively level that is less than a threshold level,which may correspond to moderate activity or activities corresponding toexercise induced heart rates of 100 beats per minute or less.

Control circuit 206 may determine the patient activity metric fordetermining a sensor indicated pacing rate for providing rate responsivepacing during increased patient activity in some examples. Theaccelerometer axis signal(s) used for determining a patient activitymetric may be filtered differently than the axis signals used fordetermining ventricular event metric(s), detecting ventricular eventsignals and/or detecting AV block. For example, motion sensor 212 mayinclude a low pass filter having an upper cutoff frequency of 10 Hz forpassing a low pass filtered patient activity signal to processor 244 fordetermining a patient activity metric. Motion sensor 212 may includebandpass filter having a lower cutoff frequency of 10 Hz or higher andan upper cutoff frequency of 30 Hz for passing a bandpass filteredcardiac motion signal from one or more of the accelerometer axes toventricular event detector circuit 240 for detecting ventricular eventsignals or more generally for determining a ventricular event metricfrom the motion signal over multiple atrial cycles.

The patient activity metric may be determined by control circuit 206 ata desired frequency, e.g., every two seconds, for use in determining asensor-indicated pacing rate (SIR) that meets the metabolic requirementsof the patient based on physical activity. The SIR may vary between theprogrammed minimum lower rate during periods of rest (minimal activitymetric) and a maximum upper pacing rate during periods of maximumexertion. The SIR may be determined according to an SIR transferfunction, which may include different rates of change of the SIR overdifferent ranges of the patient activity metric. Control circuit 206 mayenable AV block monitoring when the SIR is less than a threshold rate,the time of day is daytime, and/or the patient posture is upright, asexamples.

In some examples, the activity metric is determined as an activitycount. In these instances, control circuit 206 includes a counter thatmay track the activity count as the number of times the patient activitysignal from motion sensor 212 crosses a threshold amplitude during anactivity count interval, for example a 2-second interval. The count atthe end of each activity count interval is correlated to patient bodymotion during the activity count interval and is therefore correlated topatient metabolic demand. Example methods for obtaining an activitycount over an n-second interval are generally disclosed in U.S. Pat. No.5,720,769 (van Oort), incorporated herein by reference in its entirety.

In other examples, an activity metric may be obtained from the patientphysical activity signal by integrating or summing activity signalsample points over an activity count interval, e.g., a two-secondinterval though longer or shorter intervals of time may be used fordetermining an activity metric. The activity metric may be converted toa target heart rate to meet the patient's metabolic demand. The targetheart rate may be converted to an SIR based on an SIR transfer functionthat includes a lower rate set point and an activity of daily living(ADL) range and a maximum upper rate. Examples of methods forestablishing an SIR transfer function applied to patient activitymetrics determined from an intracardiac motion signal are generallydisclosed in U.S. Pat. No. 9,724,518 (Sheldon, et al.), incorporatedherein by reference in its entirety.

One example of an accelerometer for use in implantable medical devicesthat may be implemented in conjunction with the techniques disclosedherein is generally disclosed in U.S. Pat. No. 5,885,471 (Ruben, etal.), incorporated herein by reference in its entirety. An implantablemedical device arrangement including a piezoelectric accelerometer fordetecting patient motion is disclosed, for example, in U.S. Pat. No.4,485,813 (Anderson, et al.) and U.S. Pat. No. 5,052,388 (Sivula, etal.), both of which patents are hereby incorporated by reference hereinin their entirety. Examples of three-dimensional accelerometers that maybe implemented in pacemaker 14 and used for detecting cardiac mechanicalevents and determining ventricular event metrics using the presentlydisclosed techniques are generally described in U.S. Pat. No. 5,593,431(Sheldon) and U.S. Pat. No. 6,044,297 (Sheldon), both of which areincorporated herein by reference in their entirety. Other accelerometerdesigns may be used for producing an electrical signal that iscorrelated to motion imparted on pacemaker 14 due to ventricular andatrial mechanical events.

Sensing circuit 204 is configured to receive at least one cardiacelectrical signal via electrodes coupled to pacemaker 14, e.g.,electrodes 162 and 164. The cardiac electrical signal is received by apre-filter and amplifier circuit 220. Pre-filter and amplifier circuit220 may include a high pass filter to remove DC offset, e.g., a 2.5 to 5Hz high pass filter, or a wideband filter having a bandpass of 2.5 Hz to100 Hz or narrower to remove DC offset and high frequency noise.Pre-filter and amplifier circuit 220 may further include an amplifier toamplify the “raw” cardiac electrical signal passed to analog-to-digitalconverter (ADC) 226. ADC 226 may pass a multi-bit, digital electrogram(EGM) signal to control circuit 206 for storage in memory 210 and/orfurther analysis. For example, the EGM signal may be used by ventricularevent detector circuit 240 in identifying atrial electrical events(e.g., sensed P-waves) and/or FFRWs. Identification of FFRWs may be usedin confirming ventricular events. Identification of sensed P-wave may beused in setting windows for detecting ventricular events from the motionsignal, comparing an atrial rate to a ventricular event rate, and/ornormalizing a ventricular event metric determined from the motion signalfor detecting AV block as described below in conjunction with theaccompanying diagrams and flow charts. An episode of the EGM signalpassed to control circuit 206 from ADC 226 may be stored in memory 210in response to AV block criteria being met.

The digital signal from ADC 226 may be passed to rectifier and amplifiercircuit 222, which may include a rectifier, bandpass filter, andamplifier for passing a cardiac signal to cardiac event detector 224.Cardiac event detector 224 may include a sense amplifier or otherdetection circuitry that compares the incoming rectified, cardiacelectrical signal to a cardiac event sensing threshold, which may be anauto-adjusting threshold. For example, when the incoming signal crossesa P-wave sensing threshold, the cardiac event detector 224 produces aP-wave sensed event signal (P-sense) that is passed to control circuit206. In other examples, cardiac event detector 224 may receive thedigital output of ADC 226 for detecting P-waves by a comparator,morphological signal analysis of the digital EGM signal or other P-wavedetection techniques.

Processor 244 may provide sensing control signals to sensing circuit204, e.g., P-wave sensing threshold, sensitivity, and various blankingand refractory intervals applied to the cardiac electrical signal forcontrolling P-wave sensing. P-wave sensed event signals passed fromcardiac event detector 224 to control circuit 206 may be used forscheduling atrial pacing pulses by pace timing circuit 242 and for usein setting windows for detecting ventricular events by ventricular eventdetector circuit 240 from a signal received from motion sensor 212.P-wave sensed event signals may be used by control circuit 206 foridentifying multiple atrial cycles over which a ventricular event metricis determined for use in AV block detection.

In some examples, cardiac event detector 224 may be configured to detectFFRWs from the atrial signal received by electrodes 162 and 164. FFRWsmay be sensed based on an R-wave sensing threshold crossing, which mayoccur after an atrial pacing pulse or sensed P-wave. In other examples,control circuit 206 may detect FFRWs from the digital EGM signal passedto control circuit 206 from ADC 226. FFRWs may be detected based on amorphological analysis of the atrial EGM signal or an FFRW sensingthreshold amplitude crossing by the atrial EGM signal. Sensing circuit204 may include a P-wave sensing channel and an FFRW sensing channel.Components included in the P-wave sensing channel and the FFRW sensingchannel may be shared between both channels in some examples. Forexample, pre-filter/amplifier 220 and ADC 226 may be shared by bothchannels with the output of ADC 226 being passed to a P-wave detectorand to an FFRW detector. Different filtering and amplification may beapplied to the output of ADC 226 before passing the signal to therespective P-wave detector and FFRW detector.

In examples that include an electrode advanced to the His bundle forventricular pacing, additional electrode(s) may be coupled to cardiacelectrical signal sensing circuit 204. For example, tip electrode 184 asshown in FIGS. 3 and 4 may be coupled to sensing circuit 204 for sensingventricular R-waves by cardiac event detector 224 based on an R-wavesensing threshold crossing. In the case of pacemaker 254 which may becoupled to both an atrial lead and a ventricular lead, sensing circuit204 may include two sensing channels, one for sensing atrial P-waves andone for sensing ventricular R-waves.

Control circuit 206 includes a ventricular event detector circuit 240,pace timing circuit 242, and processor 244. Control circuit 206 mayreceive P-wave sensed event signals and/or digital cardiac electricalsignals from sensing circuit 204 for use in detecting and confirmingcardiac events and controlling atrial pacing (and in some examplesventricular pacing via the His bundle). For example, P-wave sensed eventsignals may be passed to pace timing circuit 242 for starting a newatrial pacing escape interval. In some examples, FFRW or R-wave sensedevent signals may also be passed to control circuit 206 for use indetecting or confirming ventricular events and AV block.

Ventricular event detector circuit 240 is configured to detectventricular events or determine ventricular event metric(s) from asignal received from motion sensor 212. Techniques for detectingventricular events and determining ventricular event metrics aredescribed below. In some examples, ventricular event detector circuit240 receives a motion signal from motion sensor 212 and may start aventricular event window in response to identifying an atrial event,e.g., a P-wave sensed event signal from sensing circuit 204 or an atrialpacing pulse delivered by pulse generator 202. The ventricular eventwindow may correspond to a time period after the atrial electrical eventduring which ventricular mechanical contraction is expected to occur ifAV conduction is intact. Ventricular event detector circuit 240determines if the motion sensor signal satisfies ventricular eventdetection criteria during the sensing window in some examples. Controlcircuit 206 may determine a ventricular event metric as a count ofventricular events detected over multiple atrial cycles. Processor 244may receive ventricular event detection signals from detector circuit240 for counting the detected ventricular events and determining when AVblock criteria are met. A ventricular event may be detected based on athreshold crossing by the motion signal or one or more motion signalfeatures determined during the sensing window as described below inconjunction with FIGS. 7-11 and 14 .

In other examples, control circuit 206 may determine a ventricular eventmetric over multiple atrial cycles without requiring sensing windows.For instance, the ventricular event metric may be an AV activation timein some examples, as described below in conjunction with FIGS. 12-13 .In other examples, as described below in conjunction with FIGS. 15-16 ,the ventricular event metric may include an integration metricdetermined over a detection time interval that includes multiple atrialcycles. Control circuit 206 may detect AV block, store cardiac signalepisodes, generate an alert, adjust a pacing therapy or provide otheroutput in response to the ventricular event metric meeting AV blockcriteria.

Pace timing circuit 242 may additionally receive P-wave sensed eventsignals from P-wave detector 224 for use in controlling the timing ofpacing pulses delivered by pulse generator 202. Processor 244 mayinclude one or more clocks for generating clock signals that are used bypace timing circuit 242 to time out an atrial pacing interval, e.g., apermanent lower rate pacing interval for treating bradycardia or atemporary lower rate interval for providing rate response pacing. Theatrial pacing interval, sometimes referred to as an “escape interval”may be restarted by pace timing circuit 242 in response to each atrialelectrical event, e.g., upon receipt of each P-wave sensed event signaland upon delivery of each atrial pacing pulse by pulse generator 202.

Pace timing circuit 242 may include one or more pacing rate intervaltimers or counters used to time out the pacing escape interval. Forexample, pace timing circuit 242 may include a timer or counter fortiming out the atrial pacing interval, which may be a programmableinterval stored in memory 210 and retrieved by processor 244. If aP-wave sensed event signal is not received by control circuit 206 beforeexpiration of the atrial pacing interval, pulse generator 202 generatesan atrial pacing pulse in response to the atrial pacing intervalexpiration.

In examples that include ventricular pacing capabilities by pacemaker 14(or pacemaker 254), control circuit 206 may control pulse generator 202to generate ventricular pacing pulses, e.g., delivered by a His bundlepacing electrode 184 or 284. The ventricular pacing pulses may bedelivered in a non-atrial tracking ventricular pacing mode, e.g., duringatrial tachyarrhythmia. Pace timing circuit 242 may set a ventricularpacing interval set to a lower pacing rate interval or a temporaryinterval to provide ventricular rate support. The ventricular pacingpulses may be delivered in an atrial tracking pacing mode when controlcircuit 206 detects AV block. In this case, an AV pacing interval may beset by pace timing circuit 242 in response to P-wave sensed eventsignals and atrial pacing pulses to synchronize the ventricular pacingpulses to the sensed P-waves and atrial pacing pulses. Upon expirationof an AV pacing interval, pulse generator 202 generates a ventricularpacing pulse delivered via a ventricular pacing electrode vector (e.g.,electrodes 184 and 182 shown in FIG. 3 or electrodes 284 and 282 shownin FIG. 5 ).

While only electrodes 162 and 164 are shown in FIG. 6 , it is to beunderstood from the conceptual diagrams of FIGS. 4 and 5 that anyhousing-based electrodes, e.g., electrodes 182, 184, and 186, and/orlead-based electrodes, e.g., electrodes 270, 272, 282, and 284, may beelectrically coupled to circuitry depicted in FIG. 6 and enclosed by thehousing of the pacemaker 14 or 254. As such, housing based electrodes182, 184, and 186 may be electrically coupled to pulse generator 202and/or cardiac electrical signal sensing circuit 204 for providingcardiac electrical event signal sensing and delivering pacing pulses.Lead based electrodes 270, 272, 282 and 284 shown in FIG. 5 may beelectrically coupled to pulse generator 202 and/or cardiac electricalsignal sensing circuit 204 via the conductors carried by the lead bodies266 and 268 and connector block 252.

Pulse generator 202 generates electrical pacing pulses that aredelivered to the RA of the patient's heart via cathode electrode 164 andreturn anode electrode 162 (or in other examples via electrodes 182 and186 shown in FIG. 4 or electrodes 270 and 272 shown in FIG. 5 ). Inexamples including ventricular pacing capabilities, pulse generator 202may generate electrical pacing pulses, which may be delivered to theHis-Purkinje conduction system using electrodes 184 and 182 (FIG. 4 ) orelectrodes 282 and 284 (FIG. 5 ). In addition to providing controlsignals to pace timing circuit 242 and pulse generator 202 forcontrolling the timing of atrial pacing pulses, processor 244 mayretrieve programmable pacing control parameters, such as pacing pulseamplitude and pacing pulse width, which are passed to pulse generator202 for controlling pacing pulse delivery.

Pulse generator 202 may include charging circuit 230, switching circuit232 and an output circuit 234. Charging circuit 230 is configured toreceive current from power source 214 and may include a holdingcapacitor that may be charged to a pacing pulse amplitude under thecontrol of a voltage regulator included in charging circuit 230. Thepacing pulse amplitude may be set based on a control signal from controlcircuit 206. Switching circuit 232 may control when the holdingcapacitor of charging circuit 230 is coupled to the output circuit 234for delivering the pacing pulse. For example, switching circuit 232 mayinclude a switch that is activated by a timing signal received from pacetiming circuit 242 upon expiration of a pacing escape interval and keptclosed for a programmed pacing pulse width to enable discharging of theholding capacitor of charging circuit 230. The holding capacitor,previously charged to the pacing pulse voltage amplitude, is dischargedacross electrodes 162 and 164 (or other selected pacing electrodevector) through the output capacitor of output circuit 234 for theprogrammed pacing pulse duration. Examples of pacing circuitry generallydisclosed in U.S. Pat. No. 5,507,782 (Kieval, et al.) and in U.S. Pat.No. 8,532,785 (Crutchfield, et al.), both of which patents areincorporated herein by reference in their entirety, may be implementedin pacemaker 14 (or pacemaker 254) for charging a pacing capacitor to apredetermined pacing pulse amplitude under the control of controlcircuit 206 and delivering a pacing pulse.

Memory 210 may include computer-readable instructions that, whenexecuted by control circuit 206, cause control circuit 206 to performvarious functions attributed throughout this disclosure to pacemaker 14(or pacemaker 254). The computer-readable instructions may be encodedwithin memory 210. Memory 210 may include any non-transitory,computer-readable storage media including any volatile, non-volatile,magnetic, optical, or electrical media, such as a random access memory(RAM), read-only memory (ROM), non-volatile RAM (NVRAM),electrically-erasable programmable ROM (EEPROM), flash memory, or otherdigital media with the sole exception being a transitory propagatingsignal.

Memory 210 may store sensed ventricular event data corresponding to thenumber and/or timing of ventricular events sensed by ventricular eventdetector circuit 240 from the signal from motion sensor 212. In someexamples, memory 210 includes a buffer that stores a flag for indicatingwhen no ventricular event is detected for an atrial cycle (for countingAV block cycles) and may store a flag when the ventricular event isdetected for an atrial cycle (AV conduction cycle). Memory 210 mayinclude a buffer for storing the ventricular event time for use indetecting AV block and/or detecting a trend in AV activation time formonitoring a worsening AV block condition. Memory 210 may store episodesof cardiac electrical signals sensed by sensing circuit 204 and/orepisodes of motion signals sensed by motion sensor 212 in response tocontrol circuit 206 determining that AV block criteria are met. Memory210 may additionally or alternatively store data determined by controlcircuit 206 relating to sensed cardiac events, from both the cardiacelectrical signal and the motion sensor signal, particularly datarelating to ventricular event metrics, an AV block detection, data thatcan be used for determining the percentage of time the patient is likelyin AV block and/or severity of an AV block condition.

Control circuit 206 may detect AV block when the motion signal meets AVblock criteria over multiple atrial cycles. Control circuit 206 maygenerate an alert or notification indicating the AV block detection.Telemetry circuit 208 may transmit the AV block detection notificationto external device 20. In some examples, pulse generator 202 maygenerate and deliver ventricular pacing pulses as described above inresponse to determining that AV block criteria are met or in response todetecting AV block.

Telemetry circuit 208 includes a transceiver 209 and antenna 211 fortransferring and receiving data via a radio frequency (RF) communicationlink. Telemetry circuit 208 may be capable of bi-directionalcommunication with external device 20 (FIG. 1 ) as described above.Motion sensor signals and cardiac electrical signals, and/or dataderived therefrom such as ventricular event metrics may be transmittedby telemetry circuit 208 to external device 20. Programmable controlparameters and algorithms for sensing cardiac events, including P-waves(and in some examples FFRWs or R-waves) and ventricular events from themotion signal, and for controlling pacing therapies delivered by pulsegenerator 202 may be received by telemetry circuit 208 and stored inmemory 210 for access by control circuit 206.

Power source 214 provides power to each of the other circuits andcomponents of pacemaker 14 as required. Power source 214 may include oneor more energy storage devices, such as one or more rechargeable ornon-rechargeable batteries. The connections between power source 214 andother pacemaker circuits and components are not shown in FIG. 6 for thesake of clarity but are to be understood from the general block diagramof FIG. 6 . For example, power source 214 may provide power as needed tocharging and switching circuitry included in pulse generator 202;amplifiers, ADC 226 and other components of sensing circuit 204;telemetry circuit 208; memory 210 and motion sensor 212.

The functions attributed to pacemaker 14 (and pacemaker 254) herein maybe embodied as one or more processors, controllers, hardware, firmware,software, or any combination thereof. Depiction of different features asspecific circuitry is intended to highlight different functional aspectsand does not necessarily imply that such functions must be realized byseparate hardware, firmware or software components or by any particularcircuit architecture. Rather, functionality associated with one or morecircuits described herein may be performed by separate hardware,firmware or software components, or integrated within common hardware,firmware or software components. For example, determination ofventricular event features or metrics from the motion sensor signal maybe implemented in control circuit 206 executing instructions stored inmemory 210 and relying on input from sensing circuit 204 and motionsensor 212. Providing software, hardware, and/or firmware to accomplishthe described functionality in the context of any modern pacemaker,given the disclosure herein, is within the abilities of one of skill inthe art.

FIG. 7 is a flow chart 300 of a method performed by a medical device fordetecting AV block from an intra-atrial motion signal according to oneexample. At block 302, control circuit 206 identifies multiple atrialcycles. The atrial cycles may each be identified by identifying aleading atrial event that starts the atrial cycle. The atrial eventsidentified by control circuit 206 may be atrial electrical events, e.g.,P-waves sensed by sensing circuit 204 and/or atrial pacing pulsesgenerated by pulse generator 202. In some examples, the atrial eventsare identified by control circuit 206 from the motion signal andcorrespond to atrial chamber contraction. Control circuit 206 mayidentify a predetermined number of consecutive atrial cycles in someexamples. The atrial cycles may be sampled over time, however, and arenot necessarily consecutive. In some examples, non-consecutive groups ofconsecutive atrial cycles may be identified at block 302. In oneillustrative example, three or more consecutive atrial cycles may beidentified every thirty seconds, once per minute or other samplingperiod.

At block 306, control circuit 206 determines a ventricular event metricfrom the motion sensor signal over the identified atrial cycles.Examples of ventricular event metrics are described below in conjunctionwith FIGS. 8-16 . In some examples, control circuit 206 determines if aventricular event signal is present in the motion signal received frommotion sensor 212 following each identified atrial electrical event,during each identified atrial cycle. For instance, control circuit 206may set a ventricular event sensing window in response to identifyingeach atrial event starting an associated atrial cycle. The sensingwindow may begin 100 ms or less after the atrial electrical event andend up to 500 ms or more after the atrial electrical event. The sensingwindow starting time and/or ending time may be set differently inresponse to a sensed P-wave than in response to an atrial pacing pulsebecause the timing of a ventricular contraction following an intrinsicP-wave may be different than the timing of the ventricular contractionfollowing an atrial pacing pulse. In some examples, the sensing windowstarting time and/or ending time may be adjusted based on the atrialrate, e.g., based on one or more preceding atrial cycle lengthsdetermined between two consecutively identified atrial events.

Control circuit 206 may determine the ventricular event metric at block306 by detecting the ventricular events from the motion signal presentover the atrial cycles based on a sensing threshold crossing by themotion signal within the sensing window. In other examples, one or moremotion signal features may be determined during each sensing window (orduring all or a portion of each atrial cycle) for detecting ventricularevents over the identified atrial cycles. Such motion signal featuresmay include one or more of, with no limitation intended, the ventricularevent time from the atrial event to a sensing threshold crossing, themaximum absolute peak acceleration, the maximum peak-to-peakacceleration, the maximum slope of the acceleration signal, the area ofthe acceleration signal (e.g., the integral or summation of sample pointamplitudes during the sensing window), the time from the atrialelectrical event to the maximum absolute peak acceleration, or themorphology of the overall acceleration signal waveform. A motion signalfeature or any combination of features may be determined for each atrialcycle for determining the ventricular event metric over the atrialcycles. In some examples, the motion signal feature or combination offeatures is compared to ventricular event detection criteria fordetecting each ventricular event over the atrial cycles, which mayinclude requiring that the ventricular event be detected within asensing window following each atrial event.

The ventricular event metric may be determined as a count of thedetected ventricular events over the atrial cycles, which may bereferred to as a count of AV conduction cycles. Alternatively, theventricular event metric may be determined as a count of the atrialcycles without a ventricular event detection, which may be referred toas a count of AV block cycles. Examples of techniques performed bycontrol circuit 206 for detecting a ventricular event signal duringidentified atrial cycles are described below in conjunction with FIGS.9-11 and 14 .

In some examples, determining the ventricular event metric at block 306includes updating an AV conduction cycle count and/or an AV block cyclecount. For example, an AV block cycle counter may be increased each timea ventricular event is not detected during an atrial cycle. The countervalue may be compared to an AV block threshold value at block 308. Inone example, if at least two (or other selected threshold number) of theidentified atrial electrical events are identified without detecting aventricular event following each of the two atrial electrical events,control circuit 206 may determine that AV block criteria are satisfiedat block 308. In some instances, control circuit 206 detects AV block inresponse to a threshold number of consecutive atrial cycles occurringwithout detection of the ventricular event signal from the motionsignal. An AV block cycle counter may be increased for each atrialelectrical event that is identified without detecting a ventricularevent before the next atrial electrical event (that ends the currentatrial cycle). If a ventricular event is detected during an atrial cyclebefore the AV block cycle counter value reaches an AV block detectionthreshold, control circuit 206 may reset the AV block cycle counter tozero.

In another example, control circuit 208 may set a flag indicating thedetection or absence of a ventricular event signal following each atrialelectrical event in a series of consecutive atrial electrical events. Afirst-in-first out buffer may store the value of the flag (e.g., high orlow indicating ventricular event detection or no ventricular eventdetection, respectively) for each of a series of consecutive atrialcycles. When the ventricular event is not detected from the motionsignal by ventricular event detector circuit 240 for two, three, four ormore out of a selected number of atrial cycles, e.g., six, eight, ten,twelve or other selected number of atrial cycles, AV block criteria maybe determined to be satisfied at block 308 by control circuit 206. Apercentage or ratio of the atrial cycles with no ventricular eventsignal detection out of a predetermined number of atrial cycles may bedetermined by control circuit 206 as the ventricular event metric atblock 306 and compared to AV block criteria at block 308.

In other examples, the ventricular event metric determined at block 306may be determined by control circuit 206 from the motion signal overmultiple atrial cycles without requiring setting sensing windows. Forexample, a ventricular event metric may be determined as an AVactivation time metric based on the time of the ventricular event signalduring each atrial cycle as described below in conjunction with FIGS.12-13 . In other examples, control circuit 206 may determine theventricular event metric by determining an integration metric from themotion signal over a detection time interval that includes theidentified atrial cycles. Examples of determining when AV block criteriaare met based on a ventricular event metric determined as an integrationmetric are described below in conjunction with FIGS. 15-16 .

In still other examples, the ventricular event metric may be a timeinterval over which ventricular event signals are not detected. Forexample, control circuit 206 may start a timer each time ventricularevent signal is detected and determine the time until the nextventricular event signal is detected. At block 308, control circuit 206may compare the time interval to a threshold time interval thatindicates AV block is likely. The threshold time interval may be longerduring the day than at night in some examples and/or based on the atrialrate. For example, when the time interval between two consecutivelydetected ventricular event signals is greater than three seconds orother selected threshold, AV block criteria may be determined to be metby control circuit 206 at block 308. In some examples, a longer timeinterval threshold may be set at night for determination of AV block,e.g., five seconds, six seconds or more. Determination of the timeinterval between two consecutive ventricular event signals does notnecessarily require identifying atrial cycles making block 302 optionalfor the purpose of determining when AV block criteria are met.

AV block criteria applied by control circuit 206 at block 308 mayinclude determining whether AV block is detected a threshold number oftimes or for a threshold number of consecutive sequences of atrialcycles. For example, control circuit 206 may detect AV block when theventricular event signal is detected from the motion signal on less thansix out of a sequence of eight consecutive atrial cycles for at leasttwo, three or other selected number of sequences of eight consecutiveatrial cycles. The sequences of consecutive atrial cycles may beoverlapping or non-overlapping and may be consecutive or non-consecutivesequences of atrial cycles. For instance, control circuit 206 maydetermine that the ventricular event is detected in less than athreshold number of atrial cycles in the first and third sequences of nconsecutive atrial cycles and the ventricular event is detected in morethan the threshold number of atrial cycles in the second sequence of nconsecutive atrial cycles. Control circuit 206 may determine that AVblock criteria are met at block 308 in response to the first and thirdsequences of consecutive atrial cycles having fewer than a thresholdnumber of atrial cycles associated with a detected ventricular event.

When AV block criteria are unmet at block 308, control circuit 206 mayreturn to block 302 to wait for the next atrial electrical event (orsequence of atrial events or other defined time interval) and continuemonitoring the motion signal for determining the next ventricular eventmetric. When control circuit 206 determines that AV block criteria aremet at block 308, control circuit 206 generates an output at block 310.The output may include an AV block alert or notification stored inmemory 210, which may be transmitted to external device 20 by telemetrycircuit 208. The generated output that may be stored in memory 210 andtransmitted to external device 20 may include AV block detection datadetermined by control circuit 206 and/or an associated episode of themotion signal and/or the cardiac electrical signal, both of which may bestored in memory 210 until a telemetry session is initiated. Controlcircuit 206 may determine and generate an output of AV block relateddata by determining the percentage of atrial cycles for which aventricular event was not detected by ventricular event detector circuit240, the time or total number of atrial cycles over which AV block wasdetected, the atrial rate when AV block was detected, and/or thepercentage of sensed and paced atrial events associated with noventricular event detections, as examples.

In some examples, the output generated at block 310 may include a pacingtherapy adjustment. In some cases, an atrial pacing rate may be reducedby control circuit 206 in response to AV block criteria being met.Reduction of the atrial pacing rate may promote AV conduction. Whenpacemaker 14 (or pacemaker 254) is capable of delivering ventricularpacing, as in the example configurations of FIG. 4 and FIG. 5 , controlcircuit 206 may generate an AV block detection output at block 310 byenabling pulse generator 202 to generate ventricular pacing pulses.

In some examples, when pacemaker 14 (or 254) is configured to deliverventricular pacing pulses, e.g., from an atrial implant location fordelivering His bundle pacing, pulse generator 202 may generate aventricular pacing pulse at block 310 in response to a ventricular eventnot being detected following an atrial electrical event. For instance,control circuit 206 may enable ventricular back-up pacing in response todetecting AV block. Pace timing circuit 242 may set a back-upventricular pacing interval. Pulse generator 202 may deliver aventricular pacing pulse when the back-up ventricular pacing intervalexpires without a ventricular event signal being detected (from thecardiac electrical signal as a FFRW and/or from the motion signal). Theback-up ventricular pacing interval may be started in response to themost recent preceding ventricular event detected. In other examples, theback-up ventricular pacing pulse may be delivered in response to theexpiration of a relatively long AV pacing interval, e.g. 300 ms or more,expiring without a ventricular event being detected by ventricular eventdetector circuit 240. The long AV pacing interval may be started when aP-wave is sensed by sensing circuit 204 or an atrial pacing pulse isdelivered by pulse generator 202. In this way, ventricular pacingsupport may be provided in the absence of a ventricular event during anatrial cycle. In some examples, control circuit 206 may enable deliveryof a back-up ventricular pacing pulse during each atrial cycle that aventricular event is not detected without waiting for the AV blockcriteria to be met at block 308.

In other examples, at block 310 control circuit 206 may switch thepacing mode from an atrial-only pacing mode to a pacing mode thatincludes atrial-tracking ventricular pacing in response to AV blockcriteria being met. Pace timing circuit 242 may set an AV pacinginterval in response to each atrial electrical event, and pulsegenerator 202 may generate ventricular pacing pulses when the AV pacinginterval expires without a sensed FFRW, R-wave, or mechanicalventricular event.

Enabling ventricular pacing at block 310 is optional, however. Pacemaker14 may be configured for delivering single chamber pacing to the RAwithout having ventricular pacing capabilities but may still beconfigured to detect AV block to enable other responses to AV blockcriteria being met, such as generating a notification or alert, storingAV block related data including ventricular event metric(s), motionsignal features, EGM and/or motion sensor signal episodes, and/orproviding other therapy responses. The AV block data and notificationmay be transmitted by telemetry circuit 208. The output generated atblock 310 may include storing a digital EGM signal episode and/or adigital motion signal episode associated with the AV block criteriabeing met in memory 210 for later transmission by telemetry circuit 208.To facilitate confirmation of the AV block detection and/or controllingventricular pacing therapy, the output generated by control circuit 206at block 310 may include enabling sensing circuit 204 to sense R-wavesor FFRWs from a cardiac electrical signal.

The process of FIG. 7 may be performed continuously on a beat by beatbasis for detecting whether AV conduction (or block) occurs on eachatrial cycle. In other examples, the process of FIG. 7 may be performedon a scheduled and/or triggered basis. For example, control circuit 206may perform the process of flow chart 350 at one or more scheduled timesof day for a predetermined monitoring time period or predeterminednumber of atrial cycles. The process of detecting whether AV blockcriteria are met may be scheduled to occur once, twice, three, four,six, or eight times a day, for example, and may be performed over oneminute, several minutes, one hour, two hours or other selected timeperiod or predetermined number of atrial cycles (e.g., 10 cycles, 60cycles, or more). In other examples, the process of flow chart 300 maybe performed by control circuit 206 when ventricular electrical events,e.g., R-waves or FFRWs, are not being sensed by sensing circuit 204. Forinstance, the process of flow chart 300 may be initiated by controlcircuit 206 when control circuit 206 has not received a sensedventricular event signal, corresponding to a sensed R-wave or FFRW, fromsensing circuit 204 for a predetermined number of atrial cycles or apredetermined time interval.

FIG. 8 is a flow chart 350 of a method performed by pacemaker 14 (orpacemaker 254) for detecting AV block according to another example.Pacemaker 14 may be configured to sense FFRWs from the cardiacelectrical signal received via electrodes 162 and 164. FFRWs may besensed at block 352 based on an FFRW sensing threshold crossing of thecardiac electrical signal after an atrial blanking period that mayfollow a sensed P-wave or delivered atrial pacing pulse. In someexamples, the cardiac electrical signal is filtered using two differentbandpass frequencies for enabling FFRW sensing from one filtered signaland P-wave sensing from a differently filtered signal. The near fieldP-wave generally has higher frequency components than the FFRW. Sensingcircuit 204 may include one filter having a relatively higher bandpass,e.g., 20-60 Hz, for passing P-wave signals enabling event detector 224of sensing circuit 204 to detect P-waves from the cardiac electricalsignal. Sensing circuit 204 may have a second filter having a relativelylower bandpass, e.g., 7-60 Hz, for passing FFRWs. Cardiac event detector224 may detect FFRWs from the lower bandpass filtered signal, which maybe blanked for an atrial blanking period upon each sensed P-wave. Othertechniques for sensing FFRWs may be performed by control circuit 206using the digital EGM signal received from ADC 226, which may includedetermining a signal width, signal area, peak amplitude, waveformmorphology or other signal features or combination of features forsensing FFRWs from the cardiac electrical signal. A variety oftechniques may be used for sensing FFRWs from a cardiac electricalsignal sensed from the atrial chamber. The techniques disclosed hereinare not limited to a particular method for sensing FFRWs from a cardiacelectrical signal.

Control circuit 206 may determine when FFRW sensing is lost at block354. FFRW sensing may be determined to be lost by control circuit 206when FFRWs are not being sensed in a 1:1 ratio with atrial electricalevents (i.e., sensed P-waves and atrial pacing pulses). For example,control circuit 206 may determine that FFRW sensing is lost when no FFRWis sensed during a predetermined number of consecutive atrial cycles,e.g., two, three or other predetermined number of atrial cycles. Inother examples, control circuit 206 may determine that FFRW sensing islost when no FFRW is sensed during more than a predetermined percentageof atrial cycles, e.g., when no FFRW is sensed during more than 20%, 25%or other percentage of the atrial cycles. In some examples, controlcircuit 206 detects a loss of FFRW sensing when at least X of Y atrialcycles, e.g., 2 out 8 atrial cycles, occur without a sensed FFRW.

In other examples, FFRW sensing may be suspended by control circuit 206when an atrial tachycardia or atrial fibrillation is present since FFRWsmay not be reliably sensed from an atrial EGM signal during a fastatrial rate. Suspended FFRW sensing may be determined as lost FFRWsensing at block 354.

In response to detecting a loss of FFRW sensing, control circuit 206enables sensing and analysis of the motion signal at block 356. Themotion sensor 212 may be powered down until FFRW sensing is lost in someexamples to conserve power source 214. When the loss of FFRW sensing isdetected, control circuit 206 may enable AV block detection based on themotion signal by controlling power source 214 to deliver current tomotion sensor 212. One or more axis signals of a three dimensionalaccelerometer may be selected for use in determining a ventricular eventmetric. Accordingly, each accelerometer axis selected for use by controlcircuit 206 for detecting AV block may be powered by power source 214 atblock 356.

In other examples, at least one axis of an accelerometer included inmotion sensor 212 may powered to produce an acceleration signal for usein determining a patient physical activity metric. Control circuit 206may enable AV block monitoring from the motion signal at block 356 bypowering additional accelerometer axes for producing axis signals usedfor determining motion signal features, enable bandpass filtering of oneor more accelerometer axis signals by motion sensor 212, and/or enableprocessor 244 and/or ventricular event detector circuit 240 to performprocessing and analysis of the accelerometer axis signal(s) receivedfrom motion sensor 212 for AV block detection.

At block 358, control circuit 206 may determine a ventricular eventmetric over multiple atrial cycles. In some examples, ventricular eventdetector circuit 240 may determine one or more motion signal featuresfrom the motion signal over one or more atrial cycles as described abovefor determining an AV block cycle count for comparison to AV blockcriteria at block 360. Additional examples of techniques for determiningmotion signal features for determining when AV block criteria are metare described below in conjunction with FIGS. 9-16 . When controlcircuit 206 determines that AV block criteria are unmet, control circuit206 may return to block 352. If FFRW sensing is regained (e.g., when anyof the example criteria for detecting a loss of FFRW sensing are nolonger met), control circuit 206 may power down the motion sensor orstop processing the motion signal for AV block monitoring and continuesensing FFRWs at block 352. Control circuit 206 may continue to monitorfor a loss of FFRW sensing. If a loss of FFRW sensing is still beingdetected, control circuit 206 continues to process and analyze themotion signal for determining when AV block criteria are met. If the AVblock criteria are met at block 360, control circuit 206 generates anoutput at block 362. Any of the examples given above in conjunction withFIG. 7 as responses to AV block criteria being met may be performed bycontrol circuit 206 at block 362 and may be performed in cooperationwith storing an output in memory 210, which may be used by orsubsequently passed to sensing circuit 204, pulse generator 202, and/ortelemetry circuit 208 as needed. For example, storing a cardiacelectrical signal and/or motion signal segment, adjusting a therapy,transmitting data, etc. may be included in the output generated at block362.

In other examples, instead of sensing FFRWs and enabling motion signalmonitoring for AV block when FFRW sensing is lost, control circuit 206may monitor the motion signal to detect ventricular event signals asevidence of AV conduction. When ventricular event signal sensing fromthe motion signal is lost, e.g., less than a 1:1 ratio of detectedventricular events to atrial cycles, control circuit 206 may enable FFRWsensing for confirming AV block based on an absence of FFRWs followingeach atrial event.

FIG. 9 is a diagram 400 of a cardiac electrical signal 402 andsimultaneously recorded accelerometer axis signals 410, 420 and 430during normal AV conduction. The cardiac electrical signal is an atrialEGM signal that may be produced by sensing circuit 204 from signalssensed from the patient's heart via electrodes 162 and 164. Theaccelerometer axis signals 410, 420 and 430 are rectified filteredsignals produced by motion sensor 212. Each accelerometer axis signal410, 420 and 430 may be produced from a respective axis signal of athree dimensional accelerometer included in motion sensor 212. Eachaccelerometer axis signal 410, 420 and 430 is bandpass filtered, e.g.,by a 10 to 30 Hz bandpass filter, and rectified by motion sensor 212 andpassed to control circuit 206.

Cardiac electrical signal 402 includes atrial P-waves 404, each followedby an FFRW 406. Each axis signal 410, 420, and 430 includes ventricularevent signals 412, 422 and 432, respectively, following each FFRW 406.In the example of FIG. 9 , AV conduction is intact such that each atrialP-wave 404 is conducted to the ventricles as evidenced by the FFRW 406that follows each P-wave 404 and the subsequent mechanical contractionof the ventricles as evidenced by the ventricular systolic event signals412, 422 and 432 of each axis signal 410, 420 and 430 (respectively)following each P-wave 404. The term “ventricular systolic event signals”may generally refer to signals present in the motion signal due toclosure of the tricuspid and mitral valves, ventricular contraction,and/or opening of the pulmonary and aortic valves.

As illustrated by axis signal 410, each axis signal may include aventricular diastolic event signal 421 following the ventricularsystolic event signal 412. The ventricular diastolic event signal 421may correspond to the end of ventricular systole and start ofventricular diastole with the closure of the pulmonary and aortic valvesand the ventricular relaxation and filling phase of the ventricularcycle. The techniques described herein for detecting a ventricular eventmay correspond to detecting the ventricular systolic event signals 412(or 422 or 432) corresponding to ventricular contraction because theventricular systolic event signal 412 is generally the largest amplitudesignal in the motion signal and therefore has the greatest signalstrength promoting reliable discrimination between AV conduction and AVblock. It is recognized, however, that ventricular signals of the motionsignal may include multiple signal peaks corresponding to mechanicalactivity of the ventricles during ventricular systole and/or diastole,such as the ventricular systolic signal 412 and diastolic signal 421,which may be detected when AV conduction is intact. The absence of thosesignals 412 and 421 may be evidence for detecting AV block. In someexamples, both ventricular systolic event signals and ventriculardiastolic event signals present in the motion signal may contribute to aventricular event metric determined from the motion signal fordetermining when AV block criteria are met and detecting AV block.Examples of ventricular event metrics determined from the motion signalthat may include contributions of both ventricular systolic andventricular diastolic event signals are described below, e.g., inconjunction with FIGS. 16 and 17 where the ventricular event signal isdetermined as an integration metric.

Each axis signal may include an atrial event signal 411 (as shown insignal 410) corresponding to atrial contraction subsequent to eachP-wave 404. As mentioned previously herein, in some examples, atrialcycles may be identified by identifying the atrial event signals 411from the motion signal. Since the atrial event signal 411 is relativelysmall compared to the ventricular event signals 412 and 421, however,when sensing electrodes are available in or on an atrial chamber, theatrial P-wave 404 may be a more reliable signal for identifying atrialcycles than the atrial event signal 411 of the motion signal.

Sensing circuit 204 generates a P-wave sensed event signal 408 inresponse to sensing each P-wave 404, e.g., in response to the cardiacelectrical signal 402 crossing a P-wave sensing threshold 405. Controlcircuit 206 may identify atrial cycles 407 by identifying an atrialelectrical event in response to receiving each P-wave sensed eventsignal 408. Control circuit 206 may identify multiple atrial cycles 407by identifying two consecutive atrial events associated with each atrialcycle 407. In some examples, control circuit 206 is configured toidentify an atrial cycle 407 in response to receiving a P-wave sensedevent signal 408 and, in response to receiving the P-wave sensed eventsignal, set a ventricular event sensing window 416 applied to one, twoor all three accelerometer axis signals 410, 420 and 430 or a combinedsignal determined as a combination (e.g., a summation) of any two or allthree accelerometer axis signals 410, 420 and 430. The ventricular eventsensing window 416 may be set by control circuit 206 in response to eachP-wave sensed event signal 408.

Sensing window 416 may begin without a delay at starting time 413 uponreceipt of P-wave sensed event signal 408. In other examples, sensingwindow 416 may have a starting time 413 that occurs at a predetermineddelay after the P-wave sensed event signal 408, e.g., after 50 ms, 100ms, 150 ms or other interval, which may serve to blank any atrial motionsignals, e.g., atrial event signal 411, present in the accelerometeraxis signals 410, 420 and 430 immediately following the P-wave 404.While intrinsic P-waves 404 are shown to be sensed on each atrial cyclein the example of diagram 400, it is to be understood that controlcircuit 206 may set a ventricular event sensing window 416 following anyatrial electrical event, sensed intrinsic P-wave or atrial pacing pulse,when monitoring for AV block.

In the example shown, the ventricular event sensing window 416 has anending time 417, which may be set to a predetermined time interval afterthe atrial electrical event, after P-wave sensed event signal 408 inthis example. The ending time 417 may be set to 300 ms, 400 ms, 500 ms,550 ms, 600 ms, 650 ms or other selected time interval after the atrialelectrical event. In some examples, the ending time 417 is adjustable bycontrol circuit 206 and may vary with the atrial rate, e.g., increasewith longer atrial cycles and decrease with shorter atrial cycles,and/or set differently depending on whether the atrial electrical eventis paced or sensed.

The sensing windows 416 are shown to have the same starting time 413 andending time 417 for all three axis signals 410, 420 and 430. However,the sensing windows 416 may be set uniquely for each axis signal orcombinations of signals when more than one axis signal and/orcombinations of axis signals are being used for detecting AV block. Forexample, the sensing window 416 may start earlier or later and/or endearlier or later for a particular axis signal due to the timing relativeto the P-wave sensed event signal 408 of the maximum accelerationassociated with ventricular contraction along the associated axis of themotion sensor 212.

Control circuit 206 may set a ventricular event sensing threshold 418,428, or 438 applied to a selected one, two or all three of theaccelerometer axis signals 410, 420, or 430, respectively, during thesensing window 416. In some examples, any two or all three axis signals410, 420 and 430 may be combined by control circuit 206, e.g., bysumming time-aligned sample point amplitudes of the filtered andrectified axis signals. The various operations performed by controlcircuit 206 for determining when AV block criteria are met as describedherein, including setting a sensing window 416 and setting a ventricularevent sensing threshold may be performed on the resulting signaldetermined as a combination of two or all three accelerometer axissignals 410, 420 and 430. The ventricular event sensing threshold, theselected axis signal (or combination of signals), and the sensing windowstarting and ending times may be AV block detection parameters that maybe programmable by a user using external device 20.

In response to a ventricular event threshold crossing 414, 424, or 434during the sensing window 416 by the respective accelerometer axissignal 410, 420 or 430, control circuit 206 detects the ventricularevent and determines the associated atrial cycle to be an AV conductioncycle (labeled “AVC” 437). In some examples, the ventricular eventsensing threshold may be set lower, even lower than the atrial eventpeak amplitude, and the number of sensing threshold crossings may becounted. When at least a threshold number of sensing threshold crossingsis reached during the sensing window 416 or during an atrial cycle, theatrial cycle may be determined to be an AV conduction cycle by controlcircuit 206. The threshold number of sensing threshold crossings may beone, two, three, four or more and may include only positive-goingcrossings, only negative-going crossings or both positive andnegative-going crossings.

Control circuit 206 may count an AV conduction cycle (or not count an AVblock cycle) when at least one axis signal 410, 420 or 430 crosses theventricular event threshold 418, 428 or 438 at least a threshold numberof times during the sensing window 416. In other examples, controlcircuit 206 may require that at least two or all three axis signalsand/or one or more combinations of two or all three axis signals cross arespective ventricular event threshold in order to detect the associatedatrial cycle as an AV conduction cycle. Control circuit 206 may countthe number of atrial cycles that AV conduction is not determined over apredetermined number of atrial cycles in some examples. Control circuit206 may detect AV block when a threshold number of atrial cycles areassociated with AV conduction not being determined (i.e., AV blockcycles). In some examples, control circuit 206 may set an AV block or AVconduction (AVC) flag (shown as AVC labels 437) for each atrial cycle ina buffer in memory 210 to facilitate counting atrial cycles associatedwith AV conduction determinations and/or count AV block cycles. In theexample of FIG. 400 , the ventricular event sensing threshold is crossedduring each sensing window 416 resulting in no AV block cycles andtherefore AV block criteria are determined to be unmet by controlcircuit 206 for the atrial cycles shown.

In the example of FIG. 9 , the ventricular event sensing threshold 418is set to 75 ADC units for axis signal 410, and the ventricular eventsensing thresholds 428 and 438 are set to 50 ADC units for axis signals420 and 430. One ADC unit may correspond to 11.8 milli-g (where 1 g isthe acceleration of gravity) and 100 milli-g may correspond to 1 m/s²acceleration. Accordingly a threshold of 50 to 75 ADC units maycorrespond to an acceleration of approximately 6 m/s² to approximately 9m/s². In other examples, the ventricular event threshold may be between3 m/s² and 10 m/s². The ventricular event sensing threshold may beselected for a given axis signal or combination of axis signals and maybe set differently for different single-axis signals or combinations ofaxis signals when more than one single-axis signal and/or combination ofaxis signals are being monitored for detecting AV block.

The ventricular event sensing threshold may be set and periodicallyupdated based on a maximum peak amplitude 415, 425 or 435 of one or morerespective ventricular event signals 412, 422 or 432 that are sensedfrom a respective axis signal 410, 420 or 430. The ventricular eventsensing threshold may be updated when AV conduction is being detected bycontrol circuit 206 or AV conduction is confirmed by a user interactingwith external device 20 of FIG. 1 . When a combination of two or moreaxis signals 410, 420 and 430 is used for detecting AV block the appliedsensing threshold for detecting ventricular event signals from thecombination signal may be based on a maximum peak amplitude of themotion signal determined from the combination signal during known AVconduction.

In other examples, the threshold for detecting ventricular event signalsmay be set based on lower amplitude motion signals that are not intendedto be detected, which may correspond to atrial contraction or othernon-ventricular events. The motion signal may be filtered to attenuatethe amplitude of lower amplitude signals that are not desired to besensed. The amplitude of other non-ventricular event signals (such asatrial events or baseline noise) may be determined and the threshold maybe set greater than the amplitude of non-ventricular event signals (butless than a peak amplitude of ventricular event signals).

The ventricular event sensing threshold 418, 428, or 438 may be set to apercentage of or a difference less than a mean maximum peak amplitude,median maximum peak amplitude, greatest maximum peak amplitude, leastmaximum peak amplitude, or a specified nth largest maximum peakamplitude of the motion signal that is determined by control circuit 206over a specified number of atrial cycles when AV conduction isdetermined to be intact. For example, control circuit 206 may set theventricular event sensing threshold to 50%, 60%, 70% or other selectedpercentage of a minimum (or lowest) maximum peak amplitude determinedover 3, 6, 8, 10, 12 or other specified number of atrial cycles when AVconduction is determined to be intact. Furthermore, the ventricularevent sensing threshold applied to a selected motion signal followingsensed P-waves may be set uniquely from the ventricular event sensingthreshold applied to the same motion signal following delivered atrialpacing pulses.

Control circuit 206 may be configured to determine an AV activation time440 during one or more atrial cycles. The term “AV activation time” asused herein refers to the time from an atrial electrical event (sensedP-wave or atrial pacing pulse) to a selected feature or fiducial pointof the ventricular event signal. In other examples, the AV activationtime may be determined from an atrial event, electrical or mechanical(e.g., atrial event signal 421) to the next ventricular event, which maybe the systolic event signal (e.g., signal 412) or the diastolic eventsignal (e.g., signal 421) in the motion signal. In the example of FIG. 9, control circuit 206 may determine the AV activation time 440 as thetime from the P-wave sensed event signal 408 generated by sensingcircuit 204 to the ventricular event sensing threshold crossing 414, 424or 434 by the respective ventricular systolic event signal 412, 422 or432 of a given axis signal 410, 420 or 430, respectively. A sensed AVactivation time 440 may be determined separately following P-wave sensedevent signals from a paced AV activation times determined followingatrial pacing pulses.

Control circuit 206 may determine a trend of the AV activation time 440over time to detect an increasing trend or prolongation of the AVactivation time. An increasing or increased AV activation time may be anindication of disease progression of the conduction system. Accordingly,AV activation times may be determined on a beat-by-beat basis or on asampled basis and a mean or median AV activation time may be determinedfrom a specified number of atrial cycles, e.g., 6, 8 or more atrialcycles. An hourly, daily, or weekly mean or median AV activation timemay be determined in various examples. In some examples, the AVactivation time 440 is determined for a specified number of atrialcycles or over a specified time interval at one or more scheduled timesof day or at predetermined time intervals. A mean or median AVactivation time may be determined and compared to a previouslydetermined mean or median AV activation time to determine a trend of AVactivation times. If the AV activation time trend is determined to beincreasing, e.g., an increase by more than a threshold percentage orspecified difference from a previously determined AV activation time, AVblock criteria may be determined to be met. An alert may be generated bycontrol circuit 206 to notify a clinician of the increasing trend in AVactivation time. An increasing trend in AV activation time may bedetected by control circuit 206 in response to an AV activation timebeing greater than at least one previously determined AV activationtime. An increasing trend in AV activation time, determined to meet AVblock criteria, may be determined even when other AV block criteriabased on a ventricular event metric(s) are unmet to enable controlcircuit 206 to generate a notification of a possible AV conductionabnormality or worsening condition.

In other examples, the AV activation times determined when AV blockcriteria are not met may be used in setting the starting time 413 and/orending time 417 of sensing window 416. For example, a minimum, median ormean, and/or maximum AV activation time may be determined over apredetermined number of atrial cycles and used by control circuit 206 toadjust the sensing window 416. For instance, the starting time 413 maybe adjusted to include the minimum AV activation time. The ending time417 may be adjusted to include the maximum AV activation time. Thesensing window 416 may be set to be centered on the mean or median AVactivation time. The sensing window 416 may be set by control circuit206 to a fixed duration or the duration may be adjusted (by adjustingthe starting and/or ending times 413 and 417) to include at least apredetermined percentage of all of the AV activation times determinedwhen the sensing window 416 is centered on the mean or median activationtime.

FIG. 10 is diagram 450 of a cardiac electrical signal 452 andaccelerometer axis signals 460, 470 and 480 that may be produced bypacemaker 14 during AV block. Cardiac electrical signal 450 is an atrialEGM signal produced by sensing circuit 204. Cardiac electrical signal450 includes atrial P-waves 454 and asynchronous FFRWs 456 occurring atvarying times during each atrial cycle 457 due to AV block. Eachaccelerometer axis signal 460, 470 and 480 is a rectified bandpassfiltered signal, which may be produced by motion sensor 212 from eachsignal generated by a respective axis of a three dimensionalaccelerometer. Each accelerometer signal 460, 470 and 480 includes aventricular systolic event signal 462, 472 and 482, respectively,following a FFRW 456.

Sensing circuit 204 generates a P-wave sensed event signal 458 inresponse to the cardiac electrical signal 452 crossing a P-wave sensingthreshold 455. Control circuit 206 may set a ventricular event sensingwindow 466 in response to each P-wave sensed event signal 455, asdescribed above in conjunction with FIG. 9 . Control circuit 206 mayapply the ventricular event sensing threshold 468, 478 or 488 to therespective accelerometer axis signal 460, 470 or 480 during the sensingwindow 466. As described above, a ventricular event sensing thresholdmay be applied to one, two or all three axis signals 460, 470 and 480individually and/or to a combination of two and/or all three axissignals for detecting sensing threshold crossings. Control circuit 206identifies an atrial cycle with no ventricular event sensing thresholdcrossing as an AV block cycle (AVB 485).

Control circuit 206 may identify an AV conduction cycle as any atrialcycle associated with a ventricular event sensing threshold crossingduring the sensing window 466. As described above, an AV conductioncycle may be detected by control circuit 206 when at least one axissignal 460, 470 or 480 crosses the respective sensing threshold 468, 478or 488 during the sensing window 466. In this example, an AV block cycleis identified when none of the axis signals (or a combination of axissignals) crosses the ventricular sensing threshold. In other examples,control circuit 206 may detect an AV conduction cycle when at least twoor all three axis signals cross a respective ventricular event sensingthreshold or a combination of at least two axis signals crosses aventricular event sensing threshold. In this case, control circuit 206may detect an AV block cycle as any atrial cycle during which at leastone axis signal or a combination of two or more axis signals does notcross the respective ventricular sensing threshold.

Control circuit 206 may determine a ventricular event metric as a countof AV block cycles detected over the identified atrial cycles, as apercentage of AV block cycles out of the identified atrial cycles, or asa ratio of AV block cycles to the identified atrial cycles. Tofacilitate determination of when AV block criteria are met, controlcircuit 206 may set a flag in a buffer in memory 210 indicating AV blockor AV conduction for each sensing window 466 (associated with eachatrial cycle 457). For example, a first-in-first-out buffer in memory210 may store an AVB flag or an AVC flag (shown as labels 485) for eachatrial cycle of a predetermined number of atrial cycles, e.g., 6, 8, 10,12 or other selected number of atrial cycles. After each atrial cycle457, control circuit 206 may determine if a threshold number of AVBflags are stored in the buffer. The threshold number of AVB flags may berequired to be consecutive in some examples but may be non-consecutivein other examples. In a first-in-first out buffer, the oldest AVB or AVCflag is cleared and a new flag is stored on the next atrial cycle. Inother examples, the buffer may fill with AVB or AVC flags for apredetermined number of atrial cycles and then be cleared to store AVBor AVC flags for the next predetermined number of atrial cycles. Controlcircuit 206 may determine the ventricular event metric by counting thenumber of AVB cycles each time the buffer is filled, before clearingbefore the next predetermined number of atrial cycles.

Control circuit 206 may classify a sequence of atrial cycles as AV blockin response to a threshold number of AVB flags being reached or exceededin the buffer and increment an AV block detection counter in response tothe AV block classification. When the AV block detection counter reachesa threshold, which may be one or more, AV block may be detected bycontrol circuit 206 in response to AV block criteria being met. Controlcircuit 206 may generate an output in response to the AV blockdetection, which may include storing and subsequently transmitting analert or notification and associated data and/or a therapy response.

In the examples of FIGS. 9 and 10 , the motion signal feature used todetect an AV block cycle is based on the amplitude of the motion signaland in particular the amplitude of the motion signal being less than aventricular event sensing threshold amplitude during a sensing windowfollowing each atrial electrical event. In other examples, controlcircuit 206 may determine one or more features of the motion signalduring the sensing windows 416 and 466 for determining if a ventricularevent is detected during the sensing window as evidence of AVconduction. For example, control circuit 206 may determine the maximumsignal amplitude during the sensing window, the number of peaks, thesignal width, the signal area, the maximum slope or other signalfeatures or combinations of features. One or more features may be usedto detect an AV block cycle for the associated atrial cycle. Controlcircuit 206 may determine one or more of these features to determine ifthe ventricular event signal is detected for determining a ventricularevent metric at block 306 of FIG. 7 and at block 358 of FIG. 8 .

In still other examples, an integral of the motion signal over eachsensing window 416, 466 may be determined for identifying each atrialcycle as an AVB cycle or an AVC cycle. For example, control circuit 206may sum the rectified sample point amplitudes of the motion signal oversensing window 416 or 466. Control circuit 206 may sum only sample pointamplitudes exceeding a specified minimum threshold amplitude in someexamples. The summation of the sample point amplitudes may be comparedto a threshold value for discriminating between AV block and AVconduction for a given atrial cycle. For example, when the summedamplitudes are less than the threshold, an AVB flag may be set to countthe associated cycle as an AVB cycle.

In another example, control circuit 206 may determine a count of samplepoints that exceed a specified minimum threshold amplitude in therectified motion signal during a sensing window and compare the count toa threshold count for discriminating between AV block and AV conductionatrial cycles. When the sample point count is greater than thethreshold, control circuit 206 detects the ventricular event in thesensing window, and the atrial cycle may be identified as an AVconduction cycle. When the sample point count is less than thethreshold, control circuit 206 detects an AV block cycle. The count ofAV block cycles or a ratio of AV block cycles to AV conduction cyclesmay be determined as the ventricular event metric that is compared to AVblock detection criteria by control circuit 206.

As described above in conjunction with FIG. 9 , control circuit 206 maydetermine the AV activation time 490 as the time from the P-wave sensedevent signal 458 generated by sensing circuit 204 (or from an atrialpacing pulse) to the ventricular event sensing threshold crossing by themotion signal, as shown by axis signal 460 in the example of FIG. 10 .Variability of the AV activation time 490 and/or an increasing trend inthe AV activation time 490 may be determined by control circuit 206 fordetermining when AV block criteria are met.

FIG. 11 is a flow chart 380 of a method that may be performed by amedical device for discriminating between AV block atrial cycles and AVconduction atrial cycles according to another example. Control circuit206 may perform morphological analysis of the motion signal waveform fordetermining if a ventricular event is within a sensing window set inresponse to an atrial electrical event, e.g., sensing windows 416 and466 of FIGS. 9 and 10 . Control circuit 206 may establish a ventricularevent morphology template at block 382 during known AV conduction.Telemetry circuit 208 may receive a command from a user confirming AVconduction. In other examples, control circuit 206 may detect AVconduction based on a 1:1 ratio of atrial electrical events andventricular event sensing threshold crossings during the sensing windows416 as shown in FIG. 9 .

Additionally, control circuit 206 may establish one or more P-wavemorphology metrics or features at block 382. For example, controlcircuit 206 may establish a P-wave template at block 382 from thecardiac electrical signal. One P-wave template may be established thatcorresponds to intrinsic P-waves, and another P-wave template may beestablished that corresponds to pacing-evoked P-waves in some examples.The P-wave template(s) may be established during known AV conduction. Inother examples, one or more features of the intrinsic and/orpacing-evoked P-waves may be determined as a morphology feature of anormal P-wave. Such features may include a maximum peak amplitude, aP-wave width, a maximum P-wave slope, a number of signal peaks, a P-wavearea or other distinguishing feature or combination of features of atrue P-wave signal. During AV block, the FFRW signal may occur at thesame time as or overlapping with the P-wave in the atrial EGM signalsuch that the P-wave morphology is altered compared to normal P-waves.The P-wave template and/or one or more P-wave morphology features may beestablished by control circuit 206 from the cardiac electrical signalover a P-wave morphology window that includes the time of a P-wavesensed event signal. The pacing-evoked P-wave template may beestablished by setting a P-wave morphology window in response to theatrial pacing pulse delivery.

The ventricular and/or atrial event morphology template(s) may beestablished by control circuit 206 at block 382 using wavelet transformtechniques in some examples. Wavelet transform coefficients may bedetermined from the motion signal during the sensing window, e.g., usinga Haar wavelet transform method. The digitized averaged motion sensorsignal and/or the associated wavelet transform coefficients may bestored in memory 210 as the ventricular event morphology template. Thedigitized average P-wave signal and/or the associated wavelet transformcoefficients may be stored in memory 210 as the P-wave morphologytemplate (for intrinsic and/or paced events). In other examples, themorphology template(s) may be generated from the wavelet transform of atime averaged signal acquired during confirmed AV conduction. The timeaveraged signal may be determined by determining an ensemble average ofthe motion signal (or electrical signal for the P-wave templates) frommultiple morphology sensing windows. The ensemble average may beobtained by averaging the signal within the window over the duration ofmultiple sensing windows or aligning each event signal in time based ona fiducial point of the event (ventricular event or P-wave), such as athreshold crossing or maximum peak amplitude, and averaging thetime-aligned signals. The processing performed to generate theventricular event morphology template and optionally the P-wavemorphology template(s) and compare an unknown signal to the respectivemorphology template may include other techniques in the time domain ortransformation techniques other than the wavelet transform method.

After establishing a ventricular event template during known AVconduction, control circuit 206 may begin monitoring for AV block. Atblock 384, control circuit 206 identifies an atrial cycle by identifyingan atrial electrical event and sets the ventricular event sensing windowat block 386. Control circuit 206 determines a morphology match score atblock 388. For example, the morphology match score may be determined byperforming a wavelet transform on the motion signal during theventricular event sensing window to generate a set of waveletcoefficients. The wavelet coefficients may have predetermined weightingsrepresentative of the amplitudes of the frequency components of thesignal waveform. These wavelet coefficients may be compared to thewavelet coefficients established for the ventricular event template todetermine the morphology match score.

The morphology match score represents the correlation between thewavelet coefficients of the ventricular event template corresponding toknown AV conduction and the wavelet coefficients of the unknown waveformpresent in the sensing window, which may be aligned with the templatebased on a predetermined fiducial point such as a maximum sample pointamplitude or the starting time of the sensing window and spanning thesensing window. The morphology match score may be determined usingvarious template or morphology matching techniques for determiningcorrelation between the established ventricular event template and themotion signal during unknown AV conduction status. Such techniques mayinclude various waveform correlation analyses, determination of multiplefiducial points or characteristics of the motion signal waveform duringthe sensing window such as area of the rectified signal during thesensing window, maximum peak amplitude, number of peaks or zerocrossings (prior to rectification), inflection points, peak slopes, etc.

In some examples, at block 388 control circuit 206 may determine themorphology match score between the unknown cardiac electrical signalduring an atrial morphology window and the P-wave template,corresponding to a sensed intrinsic P-wave or paced atrial cycle. Inthis case, a high morphology match score indicates a true P-wave. A lowmorphology match score may indicate a FFRW occurring concomitantly withthe P-wave, which may occur during 3rd degree AV block, for example.When this occurs, the subsequent ventricular event signal following theFFRW may appear to be synchronized to the P-wave presenting falseevidence of AV conduction. As such, detection of a low P-wave morphologymatch score or low match of other P-wave morphology features toreference P-wave morphology features, even when the ventricular eventmorphology match score determined from the motion signal is high, may beevidence of AV block. Detection of a low P-wave morphology match scorebased on the atrial EGM signal when ventricular event morphology isdetected from the motion signal may be used by control circuit 206 todiscriminate between different types of AV block and/or more accuratelytrack the frequency and duration of long ventricular pauses (when noventricular event signals are present based on one or more ventricularevent metrics).

At block 390, control circuit 206 compares the ventricular eventmorphology match score and may compare the P-wave morphology match scoreand any other determined motion signal features and/or P-wave signalfeatures to ventricular event detection criteria. The ventricularmorphology match score may be required to exceed a threshold value inorder to detect the ventricular event within the ventricular eventsensing window. For example, if the morphology match score has apossible range of 0 to 100, the match threshold may be 50, 60, 70 orother threshold value. The P-wave morphology match score may also berequired to exceed an atrial event matching threshold to verify that aFFRW is not coincident with the P-wave, e.g., less than 60, 50, 40, 30or other selected threshold. In other examples, control circuit 206 maycompare the P-wave morphology match score and/or one or more cardiacelectrical signal morphology features to established P-wave referencevalues. When the determined match score and/or cardiac electrical signalfeatures determined from a P-wave morphology window do not match thereference values, control circuit 206 may detect an altered P-wavemorphology.

When the ventricular event morphology match score is greater than athreshold score and an altered P-wave morphology is not detected, andany other determined motion signal features satisfy the ventricularevent detection criteria, AV conduction is determined to occur for thatatrial cycle. AV block is not detected for that cycle. In some examples,control circuit 206 may return to block 382 to update the ventricularelectrical event template (and optionally the P-wave template) based onthe detected ventricular event associated with AV conduction. Controlcircuit 206 may use the ventricular event signal detected at block 390to update the template at block 382. Control circuit 206 may use theP-wave signal to update the associated intrinsic or paced P-wavetemplate. The template(s) may be updated each time an AV conductioncycle is detected or periodically on a scheduled basis. When a templateupdate is not scheduled, control circuit 206 may return to block 384 toidentify the next atrial cycle to continue monitoring for AV blockcycles.

When the ventricular event morphology match score or other motion signalfeatures do not meet the ventricular event detection criteria at block390, control circuit 206 detects an AV block cycle at block 392. In someexamples, when the ventricular event morphology match score is greaterthan a match threshold score and an altered P-wave morphology isdetected, control circuit 206 may determine that ventricular eventdetection criteria are met at block 390. When ventricular eventdetection criteria are not met at block 390, control circuit 206 detectsan AV block cycle at block 392. Control circuit 206 may set an AV blockflag in a buffer in memory 210 or update an AV block counter at block394. The AV block detection for the atrial cycle based on themorphological analysis and/or other motion signal features during thesensing window may be used by control circuit 206 to determine whencriteria are met for detecting an AV block episode (block 396) andgenerating an AV block output (block 398).

The AV block episode may be detected based on criteria of a thresholdnumber of consecutive AV block cycles being detected at block 396,indicating a long ventricular pause, e.g., three consecutive AV blockcycles or more. The threshold number of AV block cycles required todetect an AV block episode manifesting as a long ventricular pause maybe set based on the atrial rate. For example, if the atrial rate is 60beats per minute, control circuit 206 may set the threshold of at leastthree consecutive AV block cycles required to detect a ventricular pausecorresponding to AV block that is at least 3 seconds long. When theatrial rate is 100 beats per minute, control circuit 206 may set thethreshold number of AV block cycles to at least five consecutive AVblock cycles to detect an AV block episode of at least three seconds. AnAV block episode may be detected by control circuit 206 at block 396when non-consecutive AV block cycles occur as threshold percentage orfrequency out of a predetermined number of atrial cycles in someexamples. When a threshold number of AV block episodes are detected (oneor more), the duration of one or more AV block episodes reaches athreshold duration, an increasing trend of AV block episode frequencyand/or duration, or other metric of AV block severity meets AV blockcriteria for providing a response to the detected AV block, controlcircuit 206 may generate a response at block 398 according to any of theexamples provided herein, such as an alert or notification,determination of total time in AV block, storage of cardiac signals,and/or adjusting a therapy according to any of the examples given above.

FIG. 12 is a diagram 500 of cardiac signals that may be sensed bypacemaker 14 in another example. Cardiac electrical signal 502 sensed bysensing circuit 204 includes atrial P-waves 504, each followed by anFFRW 506. Each accelerometer axis signal 510, 520 and 530 produced by athree-dimensional accelerometer included in motion sensor 212 isbandpass filtered and rectified by motion sensor 212 and passed tocontrol circuit 206. Each axis signal 510, 520, and 530 includesventricular systolic event signals 512, 522 and 532, respectively, eachfollowing an FFRW 506. In the example of FIG. 10 , AV conduction isintact such that each atrial P-wave 504 is conducted to the ventriclesas evidenced by the FFRW 506 that follows each P-wave 504 and thesubsequent mechanical contraction of the ventricles as evidenced by theventricular systolic event signals 512, 522 and 532 following eachP-wave 504.

Sensing circuit 204 generates a P-wave sensed event signal 508 inresponse to sensing each P-wave 504, e.g., in response to the cardiacelectrical signal 502 crossing a P-wave sensing threshold 505. In someexamples, control circuit 206 is configured to identify the maximum peakamplitude 514 of a motion sensor signal following each P-wave sensedevent signal 508 (and before the next P-wave sensed event signal oratrial pacing pulse). While intrinsic P-waves 504 are shown to be sensedon each atrial cycle in the example of diagram 500, it is to beunderstood that control circuit 206 may identify the maximum peakamplitude of a motion sensor signal following each atrial electricalevent, sensed P-wave or atrial pacing pulse. In the illustrativeexample, control circuit 206 uses the first accelerometer axis signal510 for monitoring for AV block. In this example, the maximum peakamplitude 514 is identified from accelerometer axis signal 510 duringeach atrial cycle identified based on receiving a P-wave sensed eventsignal 508 (or atrial pacing pulse during a paced atrial rhythm). Inother examples, the operations performed as described with reference toaxis signal 510 may be performed on any one, two or all three of theaxis signals 510, 520 or 530, concurrently in parallel operations orsequentially. In other examples, any two or all three axis signals 510,520 and 530 may be combined by control circuit 206, e.g., by summingtime-aligned sample point amplitudes of the filtered and rectifiedsignals. The operations performed for determining when AV block criteriaare met may be performed on the resulting signal determined as acombination of two or all three axis signals 510, 520 and 530.

Control circuit 206 may determine the amplitude 518 of each identifiedmaximum peak 514. Additionally or alternatively, control circuit 206 maydetermine the time interval 516 from each P-wave sensed event signal 508(or atrial pacing pulse) associated with the start of the atrial cycleto the subsequent maximum peak amplitude 514 (before the next atrialelectrical event). The time intervals 516 between each atrial electricalevent and the motion signal maximum peak may be analyzed by controlcircuit 206 for determining a ventricular event metric and detecting AVblock. In FIG. 12 , the time intervals 516 may be referred to as AVactivation time since they are the time from an atrial electrical eventuntil mechanical activation (contraction) of the ventricles. In someexamples, control circuit 206 may compare the AV activation time 516 toa threshold activation time for detecting AV block on a given atrialcycle. Control circuit 206 may compare the AV activation time determinedfor each identified atrial cycle to an upper threshold activation timeinterval 507. Any AV activation time longer than the upper thresholdactivation time interval 507 indicates an AV block cycle. In someexamples, control circuit 206 may compare the AV activation times to alower threshold. Any AV activation time less than the lower thresholdactivation time interval suggests a non-conducted ventricular event anddyssynchrony between the atrial electrical event and the ventricularevent as evidence of an AV block cycle. When the AV activation time 516is greater than the upper threshold time interval 507 or less than alower threshold time interval, control circuit 206 may determine that AVblock is present for that atrial cycle. In some examples, a differentupper threshold activation time interval and/or lower thresholdactivation time interval may be set following a sensed intrinsic P-wavethan following a delivered atrial pacing pulse. The AV electricalconduction time (e.g., from the P-wave to a FFRW) and therefore the AVactivation time may be different following an intrinsic P-wave thanfollowing an atrial pacing pulse. Control circuit 206 may determine aventricular event metric by counting the atrial cycles identified as AVblock cycles (having an AV activation time outside a threshold range)over a predetermined number of identified atrial cycles. If the AV blockcount reaches a threshold count, control circuit 206 may detect AVblock. The AV block counter may be reset or cleared after apredetermined number of atrial cycles or when a threshold number ofatrial cycles occur without an AV block determination.

In other examples, control circuit 206 may determine the ventricularevent metric by determining one or more metrics of the AV activationtimes determined over a predetermined number of atrial cycles. Controlcircuit 206 may determine at least one AV activation time metric that iscorrelated to the variability or other measure of spread of the AVactivation times determined over the predetermined number of atrialcycles. Additionally or alternatively, control circuit 206 may determineat least one AV activation time metric corresponding to the average orother measure of center of the AV activation times determined over thepredetermined number of atrial cycles. As examples, with no limitationsintended, control circuit 206 may determine the maximum AV activationtime, the minimum AV activation time, the average AV activation time,the median AV activation time, the range of the AV activation times, asum, average or range of successive differences between successive AVactivation times, a sum, average or range of the differences betweeneach AV activation time and the maximum, minimum, average or otherselected reference AV activation time, or any combination thereof.Control circuit 206 may compare one or more of these AV activation timemetrics to criteria for detecting AV block for the predetermined numberof atrial cycles. For example, when the AV activation time range exceedsa threshold range, AV block may be detected.

In the illustrative example of FIG. 12 , the average AV activation timeis 260 milliseconds with a range of 40 milliseconds and standarddeviation of 20 milliseconds. As can be observed in FIG. 12 , each AVactivation time 516 is similar in duration such that the range, standarddeviation, and any sum of differences between successive AV activationtimes will be relatively small. Control circuit 206 may compare these orother metrics of AV activation time to AV block criteria. For example,the average AV activation time may be compared to a threshold activationtime and the range may be compared to a threshold range. When theaverage AV activation time is less than a threshold AV activation timeassociated with normal AV conduction, e.g., less than 300 ms, and therange is less than a threshold range associated with normal AVconduction, e.g., less than 60 ms, AV block criteria are not met and AVblock is not detected by control circuit 206. Control circuit 206 maycompare one or more AV activation time metrics corresponding to centraltendency and/or spread to AV block criteria for detecting AV block overthe predetermined number of atrial cycles.

FIG. 13 is a diagram 550 of a cardiac electrical signal 552 andaccelerometer axis signals 560, 570 and 580 during AV block. Cardiacelectrical signal 552 includes P-wave signals 554 and FFRWs 556 thatoccur asynchronously with the P-wave signals 554. Sensing circuit 206generates a P-wave sensed event signal 558 in response to sensing eachP-wave signal 554. Motion sensor 212 produces filtered, rectifiedaccelerometer axis signals 560, 570 and 580, each including ventricularsystolic event signals 562, 572 and 582, respectively, corresponding toventricular contractions. As described above, control circuit 206 may beconfigured to identify the maximum peak amplitude 564 of a motion signal(axis signal 560 in the example of FIG. 13 ) following each atrialelectrical event (each P-wave sensed event signal 558 and each atrialpacing pulse when present). The maximum peaks of one, two or all threeaxis signals 560, 570 and/or 580 may be determined or the maximum peakof a combination of two or all three axis signals may be determined bycontrol circuit 206. Criteria for detecting AV block may be applied toeach axis signal 560, 570 and 580 and when at least one signal meets theAV block criteria, AV block may be detected by control circuit 206. Inother examples, at least two signals may be required to meet AV blockcriteria in order for an AV block detection to be made over apredetermined number of cycles.

The amplitude 565 of each identified maximum peak 564 may be determinedby control circuit 206 in some examples. Additionally or alternatively,the AV activation time 566 between each atrial electrical event and thesubsequent maximum peak amplitude 564 of the motion signal during theatrial cycle (before the next atrial electrical event) may be determinedby control circuit 206.

In some examples, control circuit 206 may compare each AV activationtime determined for each atrial cycle to an AV block detection thresholdtime interval or range. As observed in FIG. 13 , the AV activation times566, 567, 568 and 569 are variable, with a very short AV activation time569, which may be shorter than a lower AV activation time threshold andevidence of an asynchronous ventricular event, and a very long AVactivation time 567, which may be longer than an upper AV activationtime threshold and evidence of AV block. Each AV activation time 566,567, 568 and 569 may be compared to a threshold AV activation time 555or an AV activation time range including upper and lower limits on abeat-by-beat basis for counting atrial cycles identified as AV blockcycles having an AV activation time outside the AV activation timerange. When a threshold count of AV block cycles is reached, e.g., 2 AVblock cycles out of 6 atrial cycles or 2 AV block cycles out of 8 atrialcycles or other specified criteria, control circuit 206 may determinethat AV block criteria are met and detect AV block.

In other examples, the AV activation times may be determined for eachatrial cycle and one or more AV activation time metrics (related tocentral tendency and/or spread as described above) may be determined bycontrol circuit 206 as a ventricular event metric for comparison to AVblock criteria. In the example of FIG. 13 , the average AV activationtime is 320 ms with a range of 430 ms and standard deviation of 160 ms.In this example, the average AV activation time is greater than athreshold activation time of 300 ms, as an example, corresponding tonormal AV conduction. The large range of 430 ms is indicative of largevariability of the AV activation time indicating AV dyssynchrony. An AVactivation time range greater than a range threshold may meet AV blockcriteria. As such, in various examples, control circuit 206 may detectAV block for atrial cycles over which the AV activation time metric(s)is(are) representative of a long average AV activation time and/or largerange and/or large standard deviation or other measure of variability ofthe AV activation times, such as a coefficient of variation, the mean ofthe absolute differences between AV activation times or the like.

Control circuit 206 may compare the amplitude 565 of each identifiedmaximum peak 564 to AV block criteria in some examples. Variation in themaximum amplitude of the peak acceleration during ventricularcontraction may occur with differences in ventricular volume andpressure that may occur when the ventricles do not contract during anatrial cycle, in a 1:1 ratio with atrial cycles, or at varying timesduring the atrial cycles. In some examples, the maximum amplitude 565may be compared to a ventricular event threshold amplitude to verifythat the maximum peak corresponds to a ventricular event signal and notanother motion signal. To illustrate, in FIG. 13 , the AV activationtime 568 may not be a true activation time because the maximum peakamplitude 565 ending AV activation time 568 is very low and does notfollow an FFRW signal 556. As such, control circuit 206 may use criteriasuch as the amplitude 565 of the maximum acceleration signal peak forverifying an AV activation time.

For example, the amplitude of each maximum peak may be compared to athreshold amplitude, which may be based on one or more maximum peakamplitudes determined when AV conduction is known, e.g., based on one ormore maximum peak amplitudes 518 determined during the atrial cyclesshown in FIG. 12 . The maximum peak threshold may be set by controlcircuit 206 to a percentage, e.g., 40%, 50%, 60%, 65%, 70%, 75% or otherpercentage of the maximum peak amplitude determined when no AV block isdetected. The AV activation times 566, 567, 568 and 569 may bedetermined by control circuit 206 when the associated maximum peak hasan amplitude greater than the maximum peak threshold. Control circuit206 may ignore AV activation time 568 in this example or set the AVactivation time 568 to a maximum AV activation time (e.g., greater thana threshold activation time interval for detecting AV block) when theassociated maximum peak has an amplitude less than the maximum peakthreshold. The range or variability or other metrics of the amplitudes565 of the maximum peaks of the motion signal may be used alone or incombination with the AV activation time metric(s) for detecting AV blockover the identified atrial cycles.

FIG. 14 is a flow chart 600 of a method performed by pacemaker 14 (or254) for detecting AV block according to another example. In theexamples of FIGS. 9-10 , a ventricular event sensing window is set inresponse to each atrial electrical event. When a ventricular event isnot detected during the sensing window, AV block is determined to occurduring the associated atrial cycle. AV block criteria may be set basedon the percentage or frequency of AV block cycles. In other examples, aventricular event sensing window is not required. Ventricular events maybe detected from the motion signal and the number of ventricular events(or a corresponding ventricular rate or ventricular rate interval) maybe compared to the number of atrial cycles (or a corresponding atrialrate or atrial rate interval) over which the ventricular events weredetected. When less than a 1:1 ratio exists between ventricular eventsand atrial cycles, in other words when the ventricular event rate isless than the atrial rate, AV block may be detected by control circuit206.

At block 602 of FIG. 14 , control circuit 206 may initialize atrial andventricular event counters. The atrial event counter may be set to zeroand as atrial electrical events are identified (sensed P-waves anddelivered atrial pacing pulses) the atrial event counter may count up toa predetermined number N at block 604. Alternatively, the atrial eventcounter may be set to the predetermined number N and count down by 1each time a P-wave sensed event signal is received from sensing circuit204 or an atrial pacing pulse is delivered by pulse generator 202.

Control circuit 206 may initialize the ventricular event counter to zeroat block 602 and count up by one each time a ventricular event isdetected from the motion signal at block 606. The ventricular events maybe detected in response to a ventricular event sensing thresholdcrossing by the motion signal. For example, a positive-going crossing ofthe sensing threshold may be counted as one ventricular event. Apost-ventricular blanking period may be applied after the positive-goingcrossing to prevent the same ventricular event from being counted morethan once. The post-ventricular blanking period may be a 100 to 200 mstime interval, e.g., 120 ms to 150 ms, during which any additionalsensing threshold crossings are not counted as ventricular events.

At block 608, control circuit 206 may determine when a predeterminednumber (e.g., 3, 4, 6, 8, 10, 12, 16 or other selected number) of atrialevents (or atrial cycles) have been counted. If N atrial events have notyet been counted, control circuit 206 continues to count atrial eventsat block 604 and ventricular events at block 606 until the predeterminednumber of atrial events has been counted. When N atrial events arecounted, control circuit 206 determines the ratio of the ventricularevent count to the number of atrial events counted at block 610. Controlcircuit 206 compares the ratio to AV block criteria at block 612. Whenthe ratio is 1:1, AV block is not detected. When the ratio is less than1:1, AV block may be detected for the predetermined number of atrialcycles. In some examples, a ratio that is slightly less than 1:1 may notresult in an AV block detection to allow for slight variation inventricular event amplitude that may lead to occasional undersensing ofthe ventricular event, the occurrence of a premature ventricularcontraction which may be followed by a long pause, or other variationsin the sensed ventricular rate unrelated to AV block. For instance, whenthe ventricular event count is one or two less than the atrial eventcount, AV block may not be detected by control circuit at block 612.

A fixed number of atrial events N may be counted for detecting when theventricular rate is less than the atrial rate. As such, instead ofdetermining a ratio at block 610, control circuit 206 may compare theventricular event count to a threshold count set based on N, the fixednumber of atrial events, for determining when AV block criteria are metat block 612. The threshold may be set equal to N, equal to N−1, equalto N−2, or to a percentage of N, e.g., 80% to 100% of N. When theventricular event count is less than the threshold count, controlcircuit 206 determines that the AV block criteria are met at block 612.

In other examples, the control circuit 206 may count atrial event andventricular events over a predetermined detection time interval, e.g.,10 seconds, 20 seconds, 30 seconds, one minute, two minutes or otherselected time interval. In this case the number of atrial events willvary with atrial rate. Control circuit 206 may start the time intervalat block 602 when the atrial and ventricular event counters areinitialized and determine when the time interval is expired at block 608(instead of determining that N atrial events have been counted). Whenthe detection time interval expires, control circuit 206 determines theratio (at block 610) of the number of ventricular events counted to thenumber of atrial events counted over the predetermined time interval.The ratio is compared to AV block criteria at block 612.

When AV block criteria are unmet for the predetermined number of atrialevents (or the predetermined time interval), control circuit 206 returnsto block 602 to re-initialize the event counters and repeat the processof counting atrial events and ventricular events. When control circuit206 determines that the AV block criteria are met at block 612, AV blockmay be detected at block 614 for the predetermined number of atrialevents (or predetermined time interval including the counted atrialevents). Control circuit 206 may determine if AV block response criteriaare met at block 616. In some examples, control circuit 206 may generatean output in response to each time AV block criteria are met at block618. In other examples, control circuit 206 may determine that AV blockresponse criteria are met when AV block criteria are met a thresholdnumber of times. AV block may be required to be detected for thepredetermined number of atrial cycles (or detection time intervals) athreshold number of times before control circuit 206 generates anoutput. For instance, the AV block response criteria may be met when theAV block criteria are met for two consecutive sets of N atrial cycles ortwo consecutive detection time intervals. In other examples, at leasttwo out of three, three out of four or other X out Y sets of N atrialcycles (or N predetermined time intervals) may be required to detectedas AV block in order to meet the AV block response criteria at block616. The sets of N atrial cycles or N predetermined time interval may ormay not be required to consecutive AV block detections.

When the AV block response criteria are unmet, control circuit 206 mayreturn to block 602 without providing a response other than to count orflag the AV block detection. When AV block response criteria are met,control circuit 206 may generate an output at block 618, which mayinclude generating a notification or alert that is transmitted bytelemetry circuit 208. The output may include generating a cumulative AVblock metric. For example, control circuit 206 may update the number ofAV block detections determined over a 24 hour or other time period toprovide a metric of how much time or what percentage of the time thepatient is experiencing AV block. In some examples, a daily cumulativeAV block metric may be determined and stored in memory 210. Additionallyor alternatively, the cumulative AV block metric may be updated aftereach AV block detection to track the total time that the patient hasexperienced AV block since implantation of the pacemaker 14 (or 254).

The response generated at block 618 may include a therapy adjustmentresponse in some examples. For instance, the atrial pacing rate may bedecreased by control circuit 206 in an attempt to promote 1:1 AVconduction. In other examples, ventricular pacing (e.g., via the Hisbundle) may be enabled to provide ventricular rate support whenventricular pacing capabilities are included in the pacemaker 14 (or254). Any other examples described herein of outputs that may begenerated by control circuit 206 in response to AV block criteria beingmet may be performed at block 618, including AV block related datastorage and atrial EGM and/or motion signal episode storage.

FIG. 15 is a flow chart 700 of a method performed by a medical device,e.g., pacemaker 14 or pacemaker 254, for detecting AV block according toanother example. At block 701, control circuit 206 may establish an AVblock criteria. As described below, control circuit 206 may beconfigured to determine one or more integration metrics from the motionsignal over a detection time interval. The integration metric(s)determined over the detection time interval may be compared to the AVblock criteria for detecting AV block. For example, a ventricular eventthreshold may be set at block 701 that is applied to one or moreintegration metrics determined over the detection interval. Theventricular event threshold may be a programmable or default valuestored in memory 210. In other examples, control circuit 206 mayestablish the ventricular event threshold based on the motion signal. Inorder to establish the ventricular event threshold at block 701, controlcircuit 206 may determine a baseline integration metric of the motionsignal during known AV conduction. For example, when pacemaker 14 isinitially implanted, it is expected that the patient is not experiencingAV block and being treated for SA node dysfunction by atrial pacing onlyas needed.

During this initial post-implant time period, or when AV conduction isconfirmed by a user, control circuit 206 may determine the integrationmetric from the motion signal, using techniques described below. Theintegration metric may be determined during a detection time intervalwhen conditions for AV block monitoring are met but AV conduction ishighly likely to be intact (such as just after pacemaker implant). Forexample, AV block monitoring conditions may require that the atrial ratebe less than a threshold rate, e.g., less than 100 beats per minute,and/or require that a patient physical activity metric be below anactivity threshold. The integration metric may be determined by controlcircuit 206 over multiple integration intervals, multiple times per houror multiple times per day, for one or more days, over one week, over twoweeks, or over another selected time period. The ventricular eventthreshold may be set based on a percentage of the mean, median, orselected percentile of the integration metrics determined during periodsthat AV conduction is highly likely. To illustrate, the ventricularevent threshold may be set to the fifth percentile of the integrationmetrics determined, to the lowest integration metric determined or to apercentage of the lowest integration metric, e.g., 80%, 90%, 100%, 110%or other selected percentage of the lowest integration metric.

In this way, the ventricular event threshold is set to a level at orbelow which ventricular activity is absent or diminished as anindication of AV block. An integration metric greater than theventricular event threshold indicates ventricular activity consistentwith AV conduction. The ventricular event threshold may also be referredto as a ventricular activity threshold, ventricular motion threshold orcardiac motion threshold as it is used to discriminate betweenventricular motion during AV conduction and ventricular motion during AVblock.

At block 702, control circuit 206 may start monitoring for AV block bysetting a predetermined detection time interval, which may be started ata time that is independent of the timing of atrial events. The detectiontime interval may not be sensing window started in response to an atrialevent that is intended to encompass a single ventricular event. Rather,the detection time interval may be started anytime relative to an atrialevent or cycle and is set to a duration intended to encompass multipleatrial cycles in some examples. The detection time interval may be atleast one second long. The detection time interval may be 2, 3, 4, 5,10, 20, 30, or 60 seconds long as other examples. As indicated above,the detection time interval may be started only when AV block monitoringconditions are met, which may include specified times of day, specifiedheart rates, specified physical activity levels, and/or specifiedpatient posture.

During the detection time interval, control circuit 206 determines aventricular event metric at block 704 by determining at least oneintegration metric of the motion signal (which may be a single axissignal or combination of axis signals). The integration metric may bedetermined as a summation of sample points of the rectified, filteredsignal throughout the duration of the detection time interval. In otherexamples, multiple integration metrics may be determined over theduration of the detection time interval with each integration metricbeing determined over one integration interval that is a portion of thedetection time interval. The sample points that are summed fordetermining the integration metric may be only the sample points greaterthan a predetermined threshold amplitude or may be all sample pointsspanning the integration interval. In other examples, control circuit206 may determine the integration metric by counting the number ofsample points that are greater than a predetermined threshold amplitudeover the duration of each integration interval.

During the detection time interval, control circuit 206 may alsoidentify and count atrial cycles at block 706 in some examples. Controlcircuit 206 may count atrial cycles by counting each sensed P-wave andeach delivered atrial pacing pulse, where each atrial event isassociated with the start of an atrial cycle. In some examples, controlcircuit 206 may optionally set an atrial blanking window following eachidentified atrial event at block 708. The atrial blanking window may beset to extend from the atrial electrical event to 50 to 100 ms after theatrial electrical event. The atrial blanking window may be set to blankthe motion signal during the atrial contraction so that motion signalpeaks due to atrial contraction do not contribute to the integrationmetric. Sample points during the atrial blanking window may be ignoredby control circuit 206 and not counted or summed for determining theintegration metric. In other examples, no atrial blanking windows arerequired and all sample points spanning the integration interval may beused in determining the integration metric.

At block 710, control circuit 206 may determine if the detection timeinterval expires. Prior to expiration, control circuit 206 may continueto identify and count atrial events and continue determining theintegration metric(s) over each integration interval during thedetection time interval. When the detection time interval expires atblock 710, control circuit 206 may determine a normalized integrationmetric at block 712, in some examples. The normalized integration metricmay be determined as the integration metric divided by the number ofatrial cycles counted during the corresponding integration interval. Inother examples, counting of atrial cycles is optional. The integrationmetric may be determined without normalizing by the number of atrialcycles. For example, when the integration metric is determined overmultiple integration intervals during a detection time interval, eachintegration metric may be determined without normalizing by the numberof atrial cycles. An example method for determining multiple integrationintervals over a detection time interval is described below inconjunction with FIG. 17 .

At block 714, control circuit 206 compares the normalized integrationmetric (or non-normalized integration metric) to AV block criteria. Whenone or more ventricular events occur within an integration interval, theintegration metric, which may be normalized by the number of atrialcycles during the integration interval, is expected to be greater than aventricular event detection threshold value since the relatively largeamplitude ventricular event signals in the motion signal are expected tobe present for each one of the atrial events. When an integrationmetric, which may be normalized by the number of atrial cycles duringthe integration interval, is less than ventricular event thresholdvalue, ventricular event signals may be absent during the integrationinterval due to AV block. When the integration metric is equal to orgreater than the ventricular event threshold, evidence of at least oneventricular event signal during the integration interval may be evidencethat AV conduction is occurring during the integration interval. Assuch, when control circuit 206 determines that the integration metricdoes not meet ventricular event detection criteria, e.g., by being lessthan a predetermined ventricular event threshold value, control circuit206 may determine AV block criteria are met at block 714 for thedetection time interval (and associated atrial cycles occurring duringthe detection time interval). AV block may be detected at block 716 inresponse to the AV block criteria being met. When multiple integrationintervals define the detection time interval, a threshold number of theintegration metrics determined during the detection time interval may berequired to be less than the ventricular event threshold at block 714 tomeet AV block criteria. When the AV block criteria are unmet at block714, control circuit 206 may return to block 702 to start the nextdetection time interval, which may follow consecutively without delay orbe started after a scheduled delay time (or triggered by a loss of FFRWsensing as described above in conjunction with FIG. 8 ).

At block 718, control circuit 206 may determine if AV block responsecriteria are met after making an AV block detection at block 716. Insome examples, control circuit 206 may generate an output by storingdata in memory 210, which may be transmitted to external device 20, usedfor transmitting a notification of AV block detection, and/or providinga therapy response at block 720 according to any of the examples givedescribed herein when a single AV block detection is made. In otherexamples, at least two or more AV block detections corresponding to twoor more detection time intervals may be required, consecutively ornon-consecutively, in order to meet AV block response criteria at block718 before control circuit 206 generates an output at block 720, whichmay include storing data, transmitting an AV block notification,adjusting sensing control parameters, adjusting a therapy controlparameter or providing a therapy response.

FIG. 16 is a diagram 750 of a cardiac electrical signal 752 and motionsignal 760 spanning a detection time interval 770 according to oneexample. P-waves 754 of cardiac electrical signal 752 are sensed bysensing circuit 204, which generates the P-wave sensed event signals758. Control circuit 206 may count P-waves sensed by sensing circuit204, e.g., by counting the P-wave sensed event signals 758 (and atrialpacing pulses if present) that occur over detection time interval 770.In this example, eight P-waves are sensed and detection time interval770 may be about eight seconds long.

During the detection time interval 770, control circuit 206 determines aventricular event metric by determining an integration metric 772. Inthe example shown, detection time interval 770 includes a singleintegration interval over which the integration metric 772 isdetermined. control circuit 206 may sum the sample points of motionsignal 760 that are greater than a predetermined threshold amplitude762. Threshold amplitude 762 is shown set to about 25 ADC units, howeverhigher or lower thresholds may be used. Threshold amplitude 762 is notnecessarily set to discriminate ventricular event signals from othermotion signals but may be set to reduce the contribution of motionsignals associated with atrial systole or other non-ventricular motionsignals or baseline noise that may be present in motion signal 760. Insome examples, control circuit 206 may set an atrial blanking period 764following each atrial event. Control circuit 206 may ignore motionsignal sample points during the atrial blanking periods 764 for thepurposes of determining the integration metric 772. In some cases, botha threshold amplitude 762 and the atrial blanking period 764 are appliedto the motion signal 760 by control circuit 206 such that only motionsignal sample points having an amplitude greater than threshold 762 thatare outside atrial blanking periods 764 are used, e.g., counted orsummed, for determining the integration metric 772. In other examples,neither the threshold 762 nor the atrial blanking periods 764 areapplied. Control circuit 206 may sum the rectified amplitudes of allsample points of the filtered motion signal 760 during the detectiontime interval 770 to determine the integration metric.

The integration metric may be determined by control circuit 206 as thevalue 774 at the expiration of the detection time interval 770. Asdescribed above, control circuit 206 may normalize the integrationmetric value 774 reached at the end of the detection time interval 770by the number of atrial events counted during the detection timeinterval 770. The normalized integration metric represents a measure ofthe number or summation of motion signal sample points per atrial cycle.During 1:1 AV conduction, the normalized integration metric can beexpected to be greater than a specified threshold value, indicating thepresence of the relatively large ventricular event signal during eachatrial cycle that occurs during detection time interval 770. When AVblock is present, as in the case of the example of FIG. 16 , a largeventricular event signal is not present following each P-wave sensedevent signal 758, resulting in a relatively small integration metric 774at the expiration of the detection time interval 770. Control circuit206 may detect AV block by determining that the integration metric value774, which may be normalized by the number of atrial events or cyclesduring detection time interval 770, is less than a ventricular eventthreshold value, indicating there are no or fewer than expectedventricular events during the detection time interval 770. The thresholdvalue applied to the integration metric may be established by controlcircuit 206 during confirmed AV conduction as described above. Forexample, control circuit 206 may determine the normalized integrationmetric during known AV conduction and set the threshold value as apercentage of (or offset less than) the normalized integration metric.

FIG. 17 is a diagram 800 of a cardiac electrical signal 802 and motionsignal 810 over multiple integration intervals 822 according to oneexample. Cardiac electrical signal 802 is an atrial EGM signal includingP-waves 804 that are sensed by sensing circuit 204. Sensing circuit 204generates P-wave signals 808 in response to each sensed P-wave 804.

Motion signal 810 is a filtered, rectified signal that includes multipleatrial event signals 814, each corresponding to an atrial contractionfollowing each P-wave 804. Motion signal 810 includes ventricular eventsignals 812 when a ventricular contraction occurs. Control circuit 206may be configured to generate an integration metric signal 820 bydetermining an integration metric 816 of the motion signal 810 over eachintegration interval 822 set to a predetermined time interval, e.g., onesecond, two seconds, three seconds or other predetermined time interval.

The integration metric 816 may be determined by control circuit 206 bysumming the sample point amplitudes of the filtered, rectified motionsignal 810 during each integration interval 822. In FIG. 17 , a solidblack dot shown along motion signal 810 corresponds to the current valueof the integration metric reached for the preceding integrationinterval. While not shown in FIG. 17 , as described above in conjunctionwith FIG. 16 , control circuit 206 may set an atrial blanking periodapplied to the motion signal so that sample points during the atrialblanking period, corresponding to atrial event signals 814, are ignoredfor the purposes of determining the integration metric. Additionally oralternatively, a sample point amplitude threshold may be set by controlcircuit 206 such that any motion signal sample point having an amplitudeless than the sample point amplitude threshold is not used fordetermining the integration metric 816.

The integration metric signal 820 may be adjusted to the value of theintegration metric 816 reached at the expiration of each precedingintegration interval 822. In the example shown, the integration interval822 is one second, though longer or shorter integration intervals may beused. The summation of sample point amplitudes as it is determined bycontrol circuit 206 over the integration interval 822 is represented bythe dotted line 824. While the dotted line 824 during each integrationinterval 822 is shown as a linearly increasing value for the sake ofillustration, it is recognized that the value of the summation of samplepoint amplitudes during each integration interval 822 may increase atvarying rates as the amplitude of the motion signal 810 varies. At theexpiration of each integration interval 822, the integration metricsignal 820 is adjusted to the new integration metric value, e.g., value816, and held at that value until the expiration of the next integrationinterval, when the next integration metric value is available. The valueof the integration metric may be reset to zero upon expiration of eachintegration interval 822 to begin summing sample point amplitudes overthe next integration interval, as shown by dotted line 824.

At the expiration of the first integration interval 822, the integrationmetric signal 820 has a value set to the integration metric 816 reachedat the end of integration interval 822. It is to be understood that thesample point amplitudes of motion signal 810 may be buffered in memory210 and summed to obtain the integration metric value at the expirationof the integration interval 822. The integration metric 816 determinedfor each integration interval is correlated to the area under thefiltered, rectified motion signal during the integration interval 822that has just expired. At the expiration of each integration interval822, control circuit 206 may compare the integration metric signal 820(also represented by each solid dot along motion signal 810) to aventricular event threshold 818. The ventricular event threshold 818 maybe a user programmable value or may be established and/or adjustable bycontrol circuit 206. A method for establishing the ventricular eventthreshold 818 is described below in conjunction with FIG. 18 .

When the integration metric signal 820 is adjusted to a value greaterthan the ventricular event threshold 818 at the expiration of anintegration interval 822, control circuit 206 detects evidence of theventricular event signal 812 occurring during the integration interval822. Control circuit 206 may generate a ventricular event (VE) signal825 at the expiration of each integration interval 822 when theintegration metric signal 820 is greater than the ventricular eventthreshold 818. When the integration metric signal 820, defined as thevalue of the integration metric at the expiration of each integrationinterval 822, is less than the ventricular event threshold 818, thecontrol circuit 206 does not generate a VE signal. In some examples,control circuit 206 may generate a marker or signal indicating no VEsignal during the integration interval.

In this example, the ventricular event metric determined by controlcircuit 206 for detecting AV block may be the number of integrationintervals 822 during the detection time interval 830 that expire with noventricular event detection (each integration metric less than theventricular event threshold 818). The AV block criteria may require thata threshold number of integration intervals 822 expire with noventricular event detection during the detection interval 830. Thedetection interval 830 may include a specified number of integrationintervals 822 and extends over multiple atrial cycles. Each individualintegration interval 822 may or may not extend over multiple atrialcycles. In the example shown, the detection interval 830 is threeseconds long and includes three consecutive integration intervals 822.The duration of the detection interval 830 may be adjusted by controlcircuit 206 based on the atrial rate, the time of day, patient physicalactivity metric, patient posture, or other conditions. For example, ifthe time of day is nighttime, the detection interval 830 may be setlonger than when the time of day is daytime. In an illustrative example,the detection interval 830 is set to six seconds at night and threeseconds during the day.

In some examples, the detection interval 830 is restarted each time aventricular event is detected based on the integration metric reachingthe ventricular event threshold 818. For example, control circuit 206may restart the detection time interval 830 each time a VE signal 825 isgenerated by control circuit 206. In this case, the AV block criteriamay require that none of the consecutive integration intervals 822defining the detection time interval 830 are associated with ventricularevent detection based on the integration metric being greater than thethreshold 818. In other examples, the AV block criteria may require thata threshold number of consecutive or non-consecutive integrationintervals 822 are not associated with a ventricular event detectionwithin the detection time interval 830.

In other examples, the detection interval 830 is a moving interval thatincludes a predetermined number of the most recent integration intervals822. Control circuit 206 may determine if a threshold number ofintegration intervals 822 with no ventricular event detection is reachedthe during the moving detection time interval 830. The integrationintervals 822 with no ventricular event detection may or may not berequired to be consecutive. In some examples, control circuit 206 mayincrease a counter for each integration interval 822 that expireswithout generating a VE signal 825, e.g., without the integration metricreaching the ventricular event threshold 818, and the counter value maybe compared to a threshold count at the expiration of the detection timeinterval 830.

Control circuit 206 detects AV block in response to AV block criteriabeing met as indicated by arrow 840, based on the detection timeinterval 830 expiring with a threshold number of integration intervals822 (three in this example) not associated with a ventricular eventdetection. In the example shown, three consecutive integration metricsdo not reach the ventricular event threshold 818 resulting in AV blockdetection 840 at the expiration of the detection time interval 830. Inresponse to the AV block detection 840, control circuit 206 may start anAV block episode timer to determine the duration of the AV blockepisode.

Control circuit 206 continues to determine the integration metric overeach subsequent integration interval 822. In response to a ventricularevent detection, control circuit 206 may detect termination of the AVblock episode as indicated by arrow 842. Control circuit 206 may sum theintegration intervals from the start of the detection interval 830 thatresulted in AV block detection 840 until AV block termination 842 isdetected. In the example shown, when each integration interval is onesecond, the duration 844 of the AV block episode is seven seconds. TheAV block detection 840 may also be referred to as a “ventricular pause”detection since a long pause without a detected ventricular event basedon the motion signal 810 sensed over multiple cardiac cycles isdetected. As described above, control circuit 206 may detect a thresholdnumber of AV block episodes or long ventricular pauses based on the AVblock criteria before generation an output or response to the AV blockdetection. For example, a threshold duration of the AV block episode, athreshold frequency of AV block detections within one hour, one day, oneweek or other specified monitoring period, a threshold cumulativeduration of detected AV block episodes or other criteria may be requiredto be met before control circuit 206 generates an output or response tothe AV block detection.

FIG. 18 is a histogram 850 of integration metrics, each determined overan integration interval, e.g., as described in conjunction with FIG. 16or 17 . Control circuit 206 may establish the ventricular eventthreshold 818 by determining the integration metric for multipleintegration intervals over a set up time period which may be minutes,hours, days or weeks long. In some examples, a minimum number ofintegration metrics, e.g., 30, 60, 100, 200, 500 or other selectednumber of integration metrics may be obtained for generating a histogramof the frequency of the integration metric values.

The ventricular event threshold 818 applied to integration metricsduring AV block monitoring may be set based on a mean, median, minimumor specified percentile of the integration metric values. In oneexample, the ventricular event threshold 818 may be set by controlcircuit 206 to the fifth percentile integration metric value, the tenthpercentile or other selected percentile of the integration metrics. Inother examples, the ventricular event threshold 818 may be set bycontrol circuit 206 to the minimum integration metric or a portion,e.g., 80% or 90%, of the minimum integration metric when all integrationmetrics plotted in the histogram are highly likely to represent intactAV conduction, such as early after pacemaker implant.

In the example shown, relatively low integration metric values 852occurring at relatively low frequencies may correspond to trueventricular pauses that may be associated with AV block. Relativelyhigher integration metric values 854 occurring at the highestfrequencies likely correspond to intact AV conduction. Very highintegration metric values 858 may be considered outliers and mayrepresent noise contaminated integration intervals. In some examples,the ventricular event threshold 818 may be set based on a percentile ofthe integration metrics determined by control circuit 206 afterdiscarding outliers 858 that are greater than an upper limit 860. Oncethe ventricular event threshold is established by control circuit 206,control circuit 206 may compare integration metrics to the ventricularevent threshold 818 for identifying detection intervals determined to beAV block. When a threshold number of integration metrics fall below theventricular event threshold 818 during a detection interval, AV blockmay be detected for the detection interval as described above inconjunction with FIGS. 16 and 17 .

In some examples, control circuit 206 may store a frequency or count ofintegration metric values, each determined over an integration interval,in memory 210. The histogram, such as the histogram represented in FIG.18 , may store each integration metric over a predetermined time period,e.g., over 24 hours, one week, one month or other selected time period.The histogram data stored in memory 210 may be transmitted to externaldevice 20 for generation of a visual, graphical representation of thehistogram, e.g., on display unit 54. As described above in conjunctionwith FIG. 15 , when AV block criteria are met, e.g., when at least one(or other threshold number of) integration metric(s) is/are less than athreshold value for detecting normal ventricular activity or motion,control circuit 206 may store an episode of the atrial EGM signal and/orthe motion sensor signal.

In an illustrative example, each integration metric represented inhistogram 850 may be determined by control circuit 206 over an eightsecond integration interval (e.g., as shown and described above inconjunction with FIG. 16 ). Each eight-second integration interval maybe sequential (when the preceding integration interval ends the nextintegration interval starts) or overlapping. For instance, an eightsecond integration interval may start every one second or every twoseconds such that the eight second integration intervals are overlappingin some examples. When a threshold number of consecutive integrationintervals are less than the ventricular event threshold value, controlcircuit 206 may store a six second (or other duration) segment of theatrial EGM and/or the motion sensor signal in memory 210. The signalsegments stored in memory 210 may be transmitted to external device 20for display by display unit 54 and may be displayed with the histogramdata accumulated in memory 210 corresponding to a time period, e.g., a24 hour time period, encompassing the time of the stored signalsegments.

FIG. 19 is a flow chart 900 of a method for detecting AV block andgenerating an AV block detection output by a medical device according toanother example. At block 901, control circuit 206 determines that AVblock monitoring criteria are met. Control circuit 206 may enabledetermination of the ventricular event metric over a plurality of atrialcycles at block 902 in response to determining that at least onemonitoring condition is satisfied. For example, control circuit 206 maydetermine the time of day based on a clock included in control circuit206, determine patient posture based on a signal from the motion sensor212, determine the atrial rate based on identified atrial events, and/ordetermine a patient physical activity metric from a signal from motionsensor 212.

AV block monitoring may be suspended during nighttime hours in someinstances because AV block during sleep may be clinically lesssignificant than AV block that occurs when the patient is awake. Inaddition or instead of determining time of day, AV block monitoring maybe suspended or disabled when the patient posture is determined to be ahorizontal or non-upright posture (e.g., laying or reclined and notsitting or standing). In some examples, the patient physical activitymetric or associated SIR may be required to be less than a thresholdlevel (e.g., corresponding to rest or activities of daily living) toavoid oversensing of ventricular events due to motion signal noisecaused by patient physical activity. Additionally or alternatively, thecontrol circuit 206 may determine that the AV block monitoring criteriaare met at block 901 when the atrial rate is less than a threshold rate,e.g., less than 100 beats per minute. Example AV block monitoringcriteria may require that the time of day be specified daytime hours,patient posture is upright or non-horizontal, patient physical activityor the associated SIR is less than a threshold level, and/or the atrialrate is less than a threshold rate or any combination thereof.

In some examples, control circuit 206 may perform a check at block 901to confirm that undersensing of ventricular event signals is notsuspected before enabling AV block monitoring. For example, controlcircuit 206 may determine that ventricular event signals are detected ata threshold frequency before enabling AV block monitoring. Whenventricular event signals are not being detected or detected onlyoccasionally, the selected accelerometer axis signal or combination ofsignals and/or thresholds or criteria for detecting ventricular eventsignals may not be optimal and may lead to overdetection of AV block.

Verifying that ventricular event signals are detected at least athreshold frequency may include detecting ventricular event thresholdamplitude crossings, performing a morphology analysis of the motionsignal over a time interval associated with a threshold amplitudecrossing, determining an integration metric of the motion signal overpredetermined time intervals or number of atrial cycles, or otheranalysis to verify the presence of the ventricular event signals forpromoting reliable AV block detection. The amplitude crossings,ventricular event morphology analysis, integration metric determinationand/or other analysis may occur at any time during an atrial cycle overone atrial cycle, or over multiple atrial cycles. The criteria fordetermining a minimum frequency of ventricular event signals or thepresence of at least one ventricular event signal may be set accordingto the ventricular event metrics being determined. In some examples, thecriteria for determining if ventricular event signals are occurring maycorrespond to a minimum frequency of ventricular event signals at anexpected ventricular escape rate or junctional rate, e.g., a rate of atleast 20 to 40 ventricular events per minute. When evidence of reliablesensing of ventricular event signals is detected, control circuit 206may determine that AV block monitoring conditions are met at block 901.

In some examples, the monitoring criteria determined at block 901 bycontrol circuit 206 may be used by control circuit 206 to adjust how theventricular event metric is determined during AV block monitoring and/orfor setting the AV block criteria. For example, AV block monitoring maybe enabled when the atrial rate is less than a threshold rate, e.g.,less than 100 beats per minute or less than 90 beats per minute. Controlcircuit 206 may set a ventricular event sensing window and/orventricular event threshold applied to a given metric, e.g., anintegration metric, based on the atrial rate.

In other examples, control circuit 206 may determine the patient postureand/or the time of day. If the time of day is night and/or the patientis in a horizontal posture, control circuit 206 may set a longerdetection time interval or higher number of atrial cycles fordetermining the ventricular event metric than the detection timeinterval or number of atrial cycles used when the time of day is daytimeand the patient posture is upright. Additionally or alternatively,control circuit 206 may set the AV block criteria differently when thetime of day is daytime than when the time of day is during the night.The AV block criteria may be set differently when the patient posture isupright than when the patient posture is non-upright. For example, athreshold or other criteria for detecting AV block may be increased orgenerally made more stringent for detecting AV block at night and/or thepatient is in a horizontal position. The AV block criteria may beadjusted to a lower threshold or generally less stringent criteriaduring the day and/or when the patient is upright so that AV block ismore readily detected.

After enabling AV block monitoring at block 901 (and optionally settingany ventricular event detection and/or AV block monitoring controlparameters based on conditions checked at block 901), control circuit206 determines at least one ventricular event metric at block 902according to any of the examples described herein. Control circuit 206determines the ventricular event metric based on the motion signalsensed over multiple atrial cycles. As indicated above, the number ofatrial cycles over which the ventricular event metric is determined maybe adjusted by control circuit 206 by increasing/decreasing a number ofidentified atrial cycles or increasing/decreasing a detection timeinterval based on one or more AV block monitoring conditions in someexamples.

When control circuit 206 determines that the AV block criteria are metat block 904 based on one or more ventricular event metrics, accordingto any of the example criteria described herein, control circuit 206 maydetect an episode of AV block (which may also be considered a detectionof a long ventricular pause). Control circuit 206 may increase an AVblock episode count at block 906. Control circuit 206 may continue todetermine the ventricular event metric over multiple atrial cycles atblock 908 for determining when the ventricular event metric meets AVblock episode termination criteria at block 910.

The AV block episode termination criteria may require one or moreventricular event signals to be detected from the motion sensor signalafter detecting AV block. For instance, a single ventricular eventsignal resulting in detection of an AV conduction cycle may satisfy AVblock episode (or long ventricular pause) termination criteria. In someexamples, different criteria than the criteria applied for detecting AVblock may be applied for detecting termination. For example, a lowerpercentage of AV block cycles out of identified atrial cycles may berequired to detect termination than the percentage of AV block cyclesrequired to detect AV block. In other examples, a higher integrationmetric threshold or smaller variability in the AV activation time may berequired to detect termination than the integration metric threshold orAV activation time variability required to detect AV block. In stillother examples, termination detection may require a longer detectiontime interval or a higher number of identified atrial cycles over whichthe ventricular event metric is determined. Furthermore, control circuit206 may wait a predetermined time interval after detecting an AV blockepisode and its termination before detecting another AV block episode toavoid detecting the same AV block episode more than once and/or to avoiddetecting multiple AV block episodes due to intermittent ventricularevent sensing issues.

When one or more ventricular event metrics meet AV block episodetermination criteria at block 910, control circuit 206 may count and logthe detected episode and its duration at block 912 in memory 210 fordetermining if the AV block episode reaches AV block detection outputcriteria at block 912. For example, the duration of the AV blockepisode, the count of AV block episode detections, the total cumulativeduration of all AV block episodes detected over a specified time period,a trend in the percentage of AV block cycles, a trend in the AVactivation time duration and/or variability, or other metricscorresponding to the frequency, duration and/or severity of the AV blockepisode(s) detected by control circuit 206 may be compared to the outputcriteria at block 912. If output criteria are unmet, control circuit 206may return to block 901. If output criteria are met, control circuit 206responds to the AV block episode detection at block 914 by transmittinga notification, storing cardiac signal episodes, enabling FFRW sensing,adjusting a pacing therapy and/or other response according to any of theexamples given herein.

FIG. 20 is a flow chart 950 of a method for determining AV blockcriteria are met by at least one ventricular event metric and generatingan output in response to the AV block criteria being met according toanother example. At block 952, control circuit 206 may determineventricular event metrics during a start-up period for use inestablishing an AV block threshold (or range). The AV block thresholdmay also be referred to as a “ventricular event threshold” or“ventricular motion threshold” because the threshold is set fordiscriminating between values of the ventricular event metrics that maycorrespond to AV block (when no or few ventricular event signals arepresent in the motion signal) and values of the ventricular event metricthat may correspond to AV conduction when ventricular activity andmotion are likely to be normal or near normal. For example, controlcircuit 206 may determine any of the example ventricular event metricsdescribed herein over 1, 4, 8, 12, 24, 48 or 72 hours or other specifiedstart-up period. Control circuit 206 may establish an AV block thresholdat block 954 based on the ventricular event metrics determined duringthe start-up period. For example, during the first 24 hours afterenabling the AV block monitoring feature of pacemaker 14, controlcircuit 206 may accumulate ventricular event metrics and establish an AVblock threshold based on the ventricular event metrics, such as based ona mean, median, specified percentile, minimum or maximum value or otherrepresentative value of the ventricular event metrics (depending in parton the type of ventricular event metric being determined) that iscorrelated to a relatively low incidence of ventricular event signals inthe motion signal.

At block 956, control circuit 206 may begin AV block monitoring bydetermining the next ventricular event metric. Control circuit 206 maydetermine the ventricular event metric over multiple atrial cycles asdescribed in the various examples presented herein. When control circuit206 determines that the ventricular event metric does not meet the AVblock threshold requirement at block 958, control circuit 206 may returnto block 956 to determine the next ventricular event metric. Dependingon the ventricular event metric being determined and the correspondingAV block threshold, the ventricular event metric may be required to beless than the AV block threshold (e.g., when the ventricular eventmetric is a detected ventricular event count, integration metric, or AVconduction time). In other examples, the ventricular event metric may berequired to be greater than the AV block threshold, e.g., when theventricular event metric is an AV interval variability or standarddeviation.

When the AV block threshold is not met at block 958, control circuit 206may use the ventricular event metric to update the AV block threshold atblock 959 in some examples. In other examples, the AV block thresholdestablished at block 954 is not updated based on ventricular eventmetrics that do not meet the AV block threshold. In this case, block 959is skipped. As described below, the AV block threshold may be updatedbased on ventricular event metrics that are determined to meet AV blockcriteria, resulting in a generated AV block output by control circuit206.

When control circuit 206 determines that the ventricular event metricmeets the AV block threshold at block 958, control circuit 206 may startstoring a cardiac signal episode in memory 210. The motion signal frommotion sensor 212 may be stored in memory 210 and/or a cardiacelectrical signal received from sensing circuit 204 may be stored inmemory 210.

At block 962, control circuit 206 may determine the next ventricularevent metric, while the cardiac signal(s) continue to be acquired andwritten to memory 210. Control circuit 206 may determine a predeterminednumber of ventricular event metrics, e.g., to span a desired detectiontime interval, for use in determining when AV block criteria are metbased on the ventricular event metrics. For example, control circuit 206may determine two, three, four, five, six, ten, twelve or other selectednumber of consecutive ventricular event metrics at block 962. Eachventricular event metric may be determined over multiple atrial cycles.When a desired number of N ventricular event metrics are determined(“yes” branch of block 964), control circuit 206 may determine if the Nventricular event metrics meet AV block criteria at block 968. The Nventricular event metrics may include the first ventricular event metricdetermined at block 956 that triggered the start of cardiac signalepisode storage.

For example, control circuit 206 may determine if the number ofindividual ventricular event metrics that meet the AV block thresholdreaches a threshold number. In other examples, control circuit 206 maydetermine a mean, median, minimum, maximum, standard deviation,variability or other representative value of the N ventricular eventmetrics for comparison to a threshold or range in order to determinethat AV block criteria are met based on the ventricular event metrics.

When the AV block criteria are not met at block 968, the cardiac signalepisode being recorded in memory 210 may be discarded at block 972.Control circuit 206 may return to block 956 to determine the nextventricular event metric. When the N ventricular event metrics meet theAV block criteria as determined at block 968, control circuit 206generates the AV block output at block 970 by storing the cardiac signalepisode in memory 210 as an AV block (or low ventricular motion)episode. Since the N ventricular event metrics satisfied AV blockcriteria, the N ventricular event metrics (which may include theventricular event metric that triggered the start of cardiac signalepisode storage) may be used by control circuit 206 to update the AVblock threshold at block 959 in some examples. Control circuit 206returns to block 956 to determine the next ventricular event metric.

The AV block episode stored at block 970 may include an episode of themotion signal and/or an episode of the cardiac electrical signal that isrecorded during the determination of at least some of the N ventricularevent metrics (at block 962), starting from block 960 at the time thatthe ventricular event metric was determined to meet the AV blockthreshold (at block 958). In this way, one ventricular event metricdetermined over multiple atrial cycles may trigger the start ofrecording a cardiac signal episode in memory 210 when the ventricularevent metric meets the established AV block threshold. The cardiacsignal episode is recorded in memory as at least one more ventricularevent metric is determined. When the at least one additional ventricularevent metric meets AV block criteria, the temporarily stored cardiacsignal episode may be stored as an AV block episode, e.g., with a dateand time stamp and optionally with other ventricular event metric data.Otherwise, the cardiac signal episode may be discarded in response tothe AV block criteria not being met by the N ventricular event metricsat block 968. It is to be understood that the AV block episode may ormay not be actual AV block but does at least correspond to an episode oftime during which ventricular contribution to the motion signal isrelatively low or variable, which may be evidence of AV block.

FIG. 21 is a flow chart 1000 of a method for determining when AV blockcriteria are met based on ventricular event metrics determined asintegration metrics from the motion signal and generating an AV blockoutput in response to the integration metrics meeting the AV blockcriteria. The method of flow chart 1000 illustrates one example forperforming the method generally described above in conjunction with FIG.20 . In this example, one integration metric that is less than anestablished AV block threshold may trigger cardiac signal episodestorage. However, the cardiac signal episode may be discarded when Nintegration metrics determined over a detection time interval do notmeet AV block criteria.

At block 1002, control circuit 206 determines integration metrics fromthe motion signal during a start-up period, e.g., over an 8, 12, 24, or48 hour period or other selected time period. The integration metricsmay be determined according to any of the examples described above,e.g., in conjunction with FIGS. 15-17 . In an illustrative example,control circuit 206 sums the sample points of the filtered, rectifiedmotion signal over a two second integration time interval to obtain oneintegration metric. The integration metrics may be obtained from eachtwo-second integration time interval over a start-up period of 24 hours,as an example.

At block 1004, control circuit 206 may establish the ventricular eventthreshold, which in this example may be referred to as the AV blockthreshold because it distinguishes values of the integration metricexpected to correspond to AV conduction and values of the integrationmetric expected to correspond to AV block, as generally described abovein conjunction with FIG. 18 . Control circuit 206 may establish the AVblock threshold based on the integration metrics determined at block1002. As described above in conjunction with FIG. 18 , a ventricularevent threshold (set equal to the AV block threshold in this example)may be established as a percentile of the integration metrics, which maybe stored in a histogram in memory 210. In another example, controlcircuit 206 may determine the AV block threshold at block 1004 bydetermining a minimum average integration metric from multiple detectiontime intervals during the start-up period. For example, the detectiontime interval may be set to 8 seconds such that four 2-secondintegration metrics may be determined during each detection timeinterval during the start-up period and during subsequent AV blockmonitoring. Control circuit 206 may be configured to determine theaverage 2-second integration metric out of the four 2-second integrationmetrics determined over each 8 second detection time interval. Asdescribed above, the 8-second detection time intervals may benon-overlapping, consecutive time intervals or overlapping consecutivetime intervals in various examples. At block 1004, control circuit 206may determine the average integration metric for each detection timeinterval (when multiple integration metrics span each detection timeinterval). The AV block threshold may be based on the averageintegration metrics. In other examples, the median integration metric,nth smallest integration metric or other representative value of theintegration metrics spanning each detection time interval may bedetermined, and these representative values determined over the start-upperiod may be used for setting the AV block threshold.

In one example, control circuit 206 may determine the minimumrepresentative value of the values determined over the start-up periodat block 1004. Continuing with the example of determining the averageintegration metric over each detection time interval, control circuit206 may determine the minimum average integration metric at block 1004and establish the AV block threshold based on the minimum averageintegration metric that occurs over the start-up period. For instance,control circuit 206 may establish the AV block threshold at block 1004by summing together four consecutive 2-second integration metrics anddividing the sum by 4 to determine the average integration metric fromeach 8 second detection time interval during the start-up period.Control circuit 206 may identify the minimum average integration metricand establish the AV block threshold at block 1004 as the minimumaverage integration metric. It is to be understood that the example timeintervals given in the foregoing example are illustrative in nature andthat different time intervals and different combinations of timeintervals may be selected as the integration interval, the detectiontime interval and the start-up period used to establish the AV blockthreshold.

In other examples, control circuit 80 may establish the AV blockthreshold at block 1004 as the minimum average integration metric plusan offset or as a percentage of the minimum average integration metric.In still other examples, the AV block threshold may be set as theaverage integration metric minus an offset or as a percentage of theaverage integration metric.

After establishing the AV block threshold at block 1004, control circuit206 starts AV block monitoring by determining the next integrationmetric at block 1006, e.g., the 2-second integration metric of themotion signal. Control circuit 206 may compare the integration metric tothe AV block threshold established at block 1004, e.g., as the minimumaverage integration metric. When control circuit 206 determines that thecurrent integration metric, e.g., the 2-second integration metric, isgreater than the AV block threshold established at block 1004, controlcircuit 206 returns to block 1006 to determine the next integrationmetric.

In response to the integration metric being less than or equal to the AVblock threshold at block 1008, control circuit 206 starts recording themotion signal from motion sensor 212 and/or the cardiac electricalsignal from sensing circuit 204 in memory 210 at block 1012. In someexamples, the motion signal used to determine the integration metric atblock 1006 may be buffered in memory 210 such that the stored cardiacsignal episode may begin at the start of the integration metric thatmeets the AV block threshold requirement at block 1008. In otherexamples, the stored cardiac signal episode may begin at the start ofthe next integration interval in response to the current integrationmetric being less than or equal to the AV block threshold at block 1008.

At block 1014, control circuit 206 determines the next integrationmetric. Control circuit 206 may determine if a required number of Nintegration metrics have been determined at block 1016. In variousexamples, one, two, three, four or more integration metrics may berequired after the first integration metric that meets the AV blockthreshold to reach N integration metrics required for determining whenAV block criteria are met. In an illustrative example, control circuit206 determines three more 2-second integration metrics after the firstintegration metric that is less than or equal to the AV block thresholdso that four 2-second integration metrics spanning an 8-second detectiontime interval are determined.

When the required number of integration metrics have been determinedover the detection time interval, as determined at block 1016, controlcircuit 206 may determine the average integration metric out of the Nintegration metrics at block 1018. In other examples, a differentrepresentative value of the N integration metrics may be determinedother than the average. For example, a median, minimum, nth smallest orother representative value may be determined from the N integrationmetrics for use in determining when the N integration metrics meet AVblock criteria. Continuing the illustrative example given above, controlcircuit 80 may sum the four 2-second integration metrics determined (oneat block 1006 and three more at block 1014) and divide by four todetermine the average integration metric at block 1018. Control circuit206 may compare this average integration metric to the AV blockthreshold at block 1020. As described above, the AV block threshold isestablished at block 1004 as the minimum average integration metricdetermined from the integration metrics determined during the start-upperiod. When the average integration metric from the most recentdetection time interval is greater than the AV block threshold (“no”branch of block 1020), the cardiac signal episode stored in memory 210starting at block 1012 is discarded at block 1024. Control circuit 206returns to block 1006 to determine the next integration metric withoutdetermining that AV block criteria are met or generating an AV blockoutput.

When control circuit 206 determines that the average integration metric(or other representative value of the N integration metrics) is lessthan or equal to the AV block threshold at block 1020, control circuit206 determines that the AV block criteria are met. In response to the AVblock criteria being met, control circuit 206 generates an output atblock 1022 by storing the cardiac signal episode in memory 210 as an AVblock episode (which may also be referred to as a “low ventricularmotion” or more generally “low cardiac motion” episode since true AVblock may or may not be actually present). The cardiac signal episode isstored in memory 210, e.g., with a date and time stamp, so that it isavailable for transmission to external device 20 for review and analysisby a clinician. The cardiac signal episode may be equal to or less thanthe detection time interval corresponding to the N integration metrics.For instance, when the first integration metric that is less than the AVblock threshold triggers the start of episode storage in memory at block1012, the cardiac signal(s) may be stored over the subsequent threeintegration intervals for a total of six seconds in the illustrativeexample of four 2-second integration metrics determined over an 8-seconddetection time interval.

Control circuit 206 returns to block 1006 to determine the nextintegration metric to continue monitoring for AV block. In someexamples, the average integration metric determined at block 1018, thatis less than the AV block threshold at block 1020, may be used to updatethe AV block threshold at block 1010. For instance, the averageintegration metric determined at block 1018 that is less than thecurrent value of the AV block threshold may be determined as the newminimum average integration metric and used as the updated AV blockthreshold at block 1008 after determining the next integration metric.In other examples, the current value of the AV block threshold and thenew minimum average integration metric determined at block 1018 (that isless than the current AV block threshold) may be combined, e.g.,averaged, to determine the updated AV block threshold at block 1010.

Memory 210 may be configured to store one or more AV block episodes inresponse to the AV block criteria being met at block 1020. Since the AVblock threshold may be updated based on an average integration metricthat is less than the current AV block threshold, the cardiac signalepisode stored at block 1022 will be the AV block episode associatedwith the lowest average integration metric. The AV block episode mayoverwrite the oldest AV block episode stored when memory 210 isconfigured to store more than one cardiac signal episode.

It should be understood that, depending on the example, certain acts orevents of any of the methods described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of themethod). Moreover, in certain examples, acts or events may be performedconcurrently, e.g., through multi-threaded processing, interruptprocessing, or multiple processors, rather than sequentially. Inaddition, while certain aspects of this disclosure are described asbeing performed by a single circuit or unit for purposes of clarity, itshould be understood that the techniques of this disclosure may beperformed by a combination of units or circuits associated with, forexample, a medical device.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored as one or more instructions orcode on a computer-readable medium and executed by a hardware-basedprocessing unit. Computer-readable media may include computer-readablestorage media, which corresponds to a tangible medium such as datastorage media (e.g., RAM, ROM, EEPROM, flash memory, or any other mediumthat can be used to store desired program code in the form ofinstructions or data structures and that can be accessed by a computer).

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPLAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

Thus, a medical device has been presented in the foregoing descriptionwith reference to specific examples. It is to be understood that variousaspects disclosed herein may be combined in different combinations thanthe specific combinations presented in the accompanying drawings. It isappreciated that various modifications to the referenced examples may bemade without departing from the scope of the disclosure and thefollowing claims.

What is claimed is:
 1. A medical device comprising: a motion sensorconfigured to sense a motion signal; a control circuit configured to:determine at least one ventricular event metric from the motion signalsensed over a plurality of atrial cycles; determine that the at leastone ventricular event metric meets atrioventricular block criteria; andgenerate an output in response to determining that the ventricular eventmetric meets the atrioventricular block criteria; and a memoryconfigured to store the generated output, wherein the control circuit isconfigured to determine the at least one ventricular event metric bydetermining an integration metric based on sample point amplitudes ofthe motion signal during at least a portion of each atrial cycle of theplurality of atrial cycles.
 2. The medical device of claim 1, furthercomprising: a sensing circuit configured to sense a cardiac electricalsignal and sense P-waves from the cardiac electrical signal; and a pulsegenerator configured to generate atrial pacing pulses; wherein thecontrol circuit is configured to: determine a count of the plurality ofatrial cycles based on at least one of the P-waves sensed by the sensingcircuit and the atrial pacing pulses generated by the pulse generator;and determine the ventricular event metric by dividing the integrationmetric by the count of the plurality of atrial cycles.
 3. The medicaldevice of claim 1, wherein the control circuit is further configured to:establish a ventricular event threshold by: determining the integrationmetric for each of a plurality of integration intervals; and setting theventricular event threshold based on the determined integration metrics;wherein determining that the at least one ventricular event metric meetsthe atrioventricular block criteria comprises determining that at leastone integration metric determined from the motion signal sensed over theplurality of atrial cycles is less than the ventricular event threshold.4. The medical device of claim 1, wherein the control circuit isconfigured to: determine at least one of a time of day, an atrial rate,a patient physical activity level, and a patient posture; set adetection time interval based on at least one of the time of day, theatrial rate, the patient physical activity level, and the patientposture, where the motion signal is sensed over the plurality of atrialcycles occurring during the detection time interval.
 5. The medicaldevice of claim 1, further comprising: a sensing circuit configured tosense a cardiac electrical signal; wherein the control circuit isfurther configured to: detect an altered morphology of an atrial P-wavesensed by the sensing circuit; and determine the atrioventricular blockcriteria are met in response to detecting the altered P-wave morphology.6. The medical device of claim 1, wherein the control circuit is furtherconfigured to: set an atrial blanking window during each atrial cycle ofthe plurality of atrial cycles; and determine the ventricular eventmetric from the motion signal sensed outside the atrial blankingwindows.
 7. The medical device of claim 1, further comprising a pulsegenerator configured to deliver an adjusted pacing therapy in responseto the control circuit generating the output.
 8. The medical device ofclaim 1, further comprising: a sensing circuit configured to sense acardiac electrical signal; and a telemetry circuit; wherein the controlcircuit is configured to generate the output by storing in the memory anepisode of at least one of the cardiac electrical signal and the motionsignal in response to determining the atrioventricular block criteriaare met; and the telemetry circuit is configured to transmit the storedepisode.
 9. The medical device of claim 1, further comprising a sensingcircuit configured to sense a cardiac electrical signal, and wherein:the control circuit is configured to: determine the at least oneventricular event metric by determining an integration metric from themotion signal over each one of a plurality of integration intervals;determine that a first one of the determined integration metrics is lessthan or equal to a ventricular event threshold; start storing a cardiacsignal episode in the memory by storing at least one of the motionsignal and the cardiac electrical signal in response to determining thatthe first one of the determined integration metrics is less than orequal to the ventricular event threshold; determine that the at leastone ventricular event metric meets the atrioventricular block criteriaby: determining a representative value of the integration metricsdetermined over each one of the plurality of integration intervals; anddetermining that the representative value is less than or equal to theventricular event threshold; and generate the output by storing thecardiac signal episode extending through at least a portion of theplurality of integration intervals as an atrioventricular block episodein the memory.
 10. The medical device of claim 1, further comprising asensing circuit configured to: sense a cardiac electrical signal; andsense far field R-waves from the cardiac electrical signal wherein thecontrol circuit is further configured to: determine that far fieldR-wave sensing from the cardiac electrical signal is lost; in responseto detecting the loss of the far field R-wave sensing, enableatrioventricular block detection based on the motion signal; anddetermine the at least one ventricular event metric in response to theatrioventricular block detection being enabled.
 11. A medical devicecomprising: a motion sensor configured to sense a motion signal; acontrol circuit configured to: determine at least one feature of themotion signal during each atrial cycle of a plurality of atrial cycles;determine each atrial cycle of the plurality of atrial cycles as one ofan atrioventricular block cycle or an atrioventricular conduction cyclebased on the at least one feature of the motion signal; determine atleast one ventricular event metric from the motion signal sensed over aplurality of atrial cycles by determining a count of theatrioventricular block cycles; determine that the at least oneventricular event metric meets atrioventricular block criteria inresponse to the count of atrioventricular block cycles being greaterthan a threshold value; and generate an output in response todetermining that the ventricular event metric meets the atrioventricularblock criteria; and a memory configured to store the generated output.12. The medical device of claim 11, wherein the control circuit isfurther configured to determine the at least one ventricular eventmetric from the motion signal by: determining a fiducial point of themotion signal during each atrial cycle of the plurality of atrialcycles; for each atrial cycle of the plurality of atrial cycles,determining an atrioventricular activation time from an atrial event tothe fiducial point of the motion signal; and determining the ventricularevent metric based on the atrioventricular activation times determinedover the plurality of atrial cycles.
 13. The medical device of claim 11,further comprising a pulse generator configured to deliver an adjustedpacing therapy in response to the control circuit generating the output.14. The medical device of claim 11, further comprising: a sensingcircuit configured to sense a cardiac electrical signal; and a telemetrycircuit; wherein the control circuit is configured to generate theoutput by storing in the memory an episode of at least one of thecardiac electrical signal and the motion signal in response todetermining the atrioventricular block criteria are met; and thetelemetry circuit is configured to transmit the stored episode.
 15. Themedical device of claim 11, further comprising a sensing circuitconfigured to: sense a cardiac electrical signal; and sense far fieldR-waves from the cardiac electrical signal wherein the control circuitis further configured to: determine that far field R-wave sensing fromthe cardiac electrical signal is lost; in response to detecting the lossof the far field R-wave sensing, enable atrioventricular block detectionbased on the motion signal; and determine the at least one ventricularevent metric in response to the atrioventricular block detection beingenabled.
 16. A medical device comprising: a motion sensor configured tosense a motion signal; a control circuit configured to: detect acondition for monitoring for atrioventricular block; determine at leastone ventricular event metric from the motion signal sensed over aplurality of atrial cycles in response to detecting the condition formonitoring for atrioventricular block; determine that the at least oneventricular event metric meets atrioventricular block criteria; andgenerate an output in response to determining that the ventricular eventmetric meets the atrioventricular block criteria; and a memoryconfigured to store the generated output.
 17. The medical device ofclaim 16, further comprising a pulse generator configured to deliver anadjusted pacing therapy in response to the control circuit generatingthe output.
 18. The medical device of claim 16, further comprising: asensing circuit configured to sense a cardiac electrical signal; and atelemetry circuit; wherein the control circuit is configured to generatethe output by storing in the memory an episode of at least one of thecardiac electrical signal and the motion signal in response todetermining the atrioventricular block criteria are met; and thetelemetry circuit is configured to transmit the stored episode.
 19. Amethod, comprising: sensing a motion signal; determining at least oneventricular event metric from the motion signal sensed over a pluralityof atrial cycles; determining that the at least one ventricular eventmetric meets atrioventricular block criteria; generating an output inresponse to determining the atrioventricular block criteria are met; andstoring the generated output, wherein determining the at least oneventricular event metric comprises determining an integration metricbased on sample point amplitudes of the motion signal during at least aportion of each atrial cycle of the plurality of atrial cycles.
 20. Themethod of claim 19, further comprising: sensing a cardiac electricalsignal; sensing P-waves from the cardiac electrical signal; generatingatrial pacing pulses; determining a count of the plurality of atrialcycles based on at least one of the sensed P-waves and the atrial pacingpulses; and determining the ventricular event metric by dividing theintegration metric by the count of the plurality of atrial cycles. 21.The method of claim 19, further comprising: establishing a ventricularevent threshold by: determining the integration metric for each of aplurality of integration intervals; and setting the ventricular eventthreshold based on the determined integration metrics; whereindetermining that the at least one ventricular event metric meets theatrioventricular block criteria comprises determining that at least oneintegration metric determined from the motion signal sensed over theplurality of atrial cycles is less than the ventricular event threshold.22. The method of claim 19, further comprising: determining at least oneof a time of day, an atrial rate, a patient physical activity level, anda patient posture; setting a detection time interval based on at leastone of the time of day, the atrial rate, the patient physical activitylevel, and the patient posture, where the motion signal is sensed overthe plurality of atrial cycles occurring during the detection timeinterval.
 23. The method of claim 19, further comprising: determining atleast one feature of the motion signal during each atrial cycle of theplurality of cycles; determining each atrial cycle of the plurality ofatrial cycles as one of an atrioventricular block cycle or anatrioventricular conduction cycle based on the at least one feature ofthe motion signal; determining the ventricular event metric bydetermining a count of the atrioventricular block cycles; anddetermining that the ventricular event metric meets atrioventricularblock criteria in response to the count of atrioventricular block cyclesbeing greater than a threshold value.
 24. The method of claim 19,further comprising: sensing a cardiac electrical signal; detecting analtered morphology of an atrial P-wave sensed from the cardiacelectrical signal; and determining the atrioventricular block criteriaare met in response to detecting the altered P-wave morphology.
 25. Themethod of claim 19, wherein determining the at least one ventricularevent metric from the motion signal comprises: determining a fiducialpoint of the motion signal during each atrial cycle of the plurality ofatrial cycles; for each atrial cycle of the plurality of atrial cycles,determining an atrioventricular activation time from an atrial event tothe fiducial point of the motion signal; and determining the ventricularevent metric based on the atrioventricular activation times determinedover the plurality of atrial cycles.
 26. The method of claim 19, furthercomprising: setting an atrial blanking window during each atrial cycleof the plurality of atrial cycles; and determining the ventricular eventmetric from the motion signal sensed outside the atrial blankingwindows.
 27. The method of claim 19, further comprising adjusting apacing therapy in response to generating the output.
 28. The method ofclaim 19, further comprising: sensing a cardiac electrical signal;generating the output by storing an episode of at least one of thecardiac electrical signal and the motion signal in response todetermining the atrioventricular block criteria are met; andtransmitting the stored episode.
 29. The method of claim 19, furthercomprising: detecting a condition for monitoring for atrioventricularblock; and determining the at least one ventricular event metric fromthe motion signal in response to detecting the condition for monitoringfor atrioventricular block.
 30. The method of claim 19, furthercomprising: sensing a cardiac electrical signal; determining the atleast one ventricular event metric by determining an integration metricfrom the motion signal over each one of a plurality of integrationintervals; determining that a first one of the determined integrationmetrics is less than or equal to a ventricular event threshold; startingstorage of a cardiac signal episode in the memory by storing at leastone of the motion signal and the cardiac electrical signal in responseto determining that the first one of the determined integration metricsis less than or equal to the ventricular event threshold; determiningthat the at least one ventricular event metric meets theatrioventricular block criteria by: determining a representative valueof the integration metrics determined over each one of the plurality ofintegration intervals; and determining that the representative value isless than or equal to the ventricular event threshold; and generatingthe output by storing the cardiac signal episode extending through atleast a portion of the plurality of integration intervals as anatrioventricular block episode in the memory.
 31. A non-transitory,computer-readable storage medium comprising a set of instructions which,when executed by a control circuit of a medical device, cause themedical device to: sense a motion signal; determine at least oneventricular event metric from the motion signal sensed over a pluralityof atrial cycles by determining an integration metric based on samplepoint amplitudes of the motion signal during at least a portion of eachatrial cycle of the plurality of atrial cycles; determine that the atleast one ventricular event metric meets atrioventricular blockcriteria; generate an output in response to determining theatrioventricular block; and store the output in a memory of the medicaldevice.